diff --git a/day11/Cargo.lock b/day11/Cargo.lock
new file mode 100644
index 0000000..4ab9be8
--- /dev/null
+++ b/day11/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day11"
+version = "0.1.0"
diff --git a/day11/Cargo.toml b/day11/Cargo.toml
new file mode 100644
index 0000000..8f5b9a5
--- /dev/null
+++ b/day11/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day11"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day11/input.txt b/day11/input.txt
new file mode 100644
index 0000000..ef22f88
--- /dev/null
+++ b/day11/input.txt
@@ -0,0 +1,55 @@
+Monkey 0:
+  Starting items: 66, 79
+  Operation: new = old * 11
+  Test: divisible by 7
+    If true: throw to monkey 6
+    If false: throw to monkey 7
+
+Monkey 1:
+  Starting items: 84, 94, 94, 81, 98, 75
+  Operation: new = old * 17
+  Test: divisible by 13
+    If true: throw to monkey 5
+    If false: throw to monkey 2
+
+Monkey 2:
+  Starting items: 85, 79, 59, 64, 79, 95, 67
+  Operation: new = old + 8
+  Test: divisible by 5
+    If true: throw to monkey 4
+    If false: throw to monkey 5
+
+Monkey 3:
+  Starting items: 70
+  Operation: new = old + 3
+  Test: divisible by 19
+    If true: throw to monkey 6
+    If false: throw to monkey 0
+
+Monkey 4:
+  Starting items: 57, 69, 78, 78
+  Operation: new = old + 4
+  Test: divisible by 2
+    If true: throw to monkey 0
+    If false: throw to monkey 3
+
+Monkey 5:
+  Starting items: 65, 92, 60, 74, 72
+  Operation: new = old + 7
+  Test: divisible by 11
+    If true: throw to monkey 3
+    If false: throw to monkey 4
+
+Monkey 6:
+  Starting items: 77, 91, 91
+  Operation: new = old * old
+  Test: divisible by 17
+    If true: throw to monkey 1
+    If false: throw to monkey 7
+
+Monkey 7:
+  Starting items: 76, 58, 57, 55, 67, 77, 54, 99
+  Operation: new = old + 6
+  Test: divisible by 3
+    If true: throw to monkey 2
+    If false: throw to monkey 1
diff --git a/day11/src/main.rs b/day11/src/main.rs
new file mode 100644
index 0000000..543560c
--- /dev/null
+++ b/day11/src/main.rs
@@ -0,0 +1,158 @@
+use std::num::ParseIntError;
+use std::env;
+use std::fs::File;
+use std::io::{self, BufRead, Lines};
+use std::collections::VecDeque;
+
+#[derive(Debug)]
+enum Operator { Add, Mul }
+#[derive(Debug)]
+enum Operand { Old, Imm(u64) }
+
+#[derive(Debug)]
+struct Operation { left: Operand, op: Operator, right: Operand }
+impl Operation {
+    fn perform(&self, old: u64) -> u64 {
+        let left = match self.left {
+            Operand::Old => old,
+            Operand::Imm(x) => x,
+        };
+        let right = match self.right {
+            Operand::Old => old,
+            Operand::Imm(x) => x,
+        };
+        match self.op {
+            Operator::Add => left + right,
+            Operator::Mul => left * right,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Monkey {
+    id: u64,
+    items: VecDeque<u64>,
+    operation: Operation,
+    div_by_test: u64,
+    true_throw: u64,
+    false_throw: u64,
+}
+
+#[derive(Debug)]
+enum MonkeyError {
+    ParseError(),
+    ParseIntError(ParseIntError),
+    IoError(io::Error),
+}
+impl From<ParseIntError> for MonkeyError {
+    fn from(e: ParseIntError) -> Self { MonkeyError::ParseIntError(e) }
+}
+impl From<io::Error> for MonkeyError {
+    fn from(e: io::Error) -> Self { MonkeyError::IoError(e) }
+}
+
+fn parse_monkey<B: BufRead>(
+    lines: &mut Lines<B>
+) -> Result<Option<Monkey>, MonkeyError> {
+    let id = match lines.next() {
+        Some(line) => line?
+            .strip_prefix("Monkey ").ok_or(MonkeyError::ParseError())?
+            .strip_suffix(":").ok_or(MonkeyError::ParseError())?
+            .parse::<u64>()?,
+        None => return Ok(None),
+    };
+
+    let starting_items = lines.next().ok_or(MonkeyError::ParseError())??
+        .strip_prefix("  Starting items: ").ok_or(MonkeyError::ParseError())?
+        .split(", ")
+        .map(|item| item.parse::<u64>())
+        .collect::<Result<VecDeque<_>, _>>()?;
+
+    let op_line = lines.next().ok_or(MonkeyError::ParseError())??;
+    let op_vec = op_line
+        .strip_prefix("  Operation: new = ").ok_or(MonkeyError::ParseError())?
+        .split(' ').collect::<Vec<_>>();
+    let (left, operator, right) = (op_vec[0], op_vec[1], op_vec[2]);
+    let operation = Operation {
+        left: match left {
+            "old" => Operand::Old,
+            _ => Operand::Imm(left.parse()?)
+        },
+        op: match operator {
+            "+" => Ok(Operator::Add),
+            "*" => Ok(Operator::Mul),
+            _ => Err(MonkeyError::ParseError())
+        }?,
+        right: match right {
+            "old" => Operand::Old,
+            _ => Operand::Imm(right.parse()?)
+        },
+    };
+        
+    let test_val = lines.next().ok_or(MonkeyError::ParseError())??
+        .strip_prefix("  Test: divisible by ").ok_or(MonkeyError::ParseError())?
+        .parse::<u64>()?;
+
+    let true_throw = lines.next().ok_or(MonkeyError::ParseError())??
+        .strip_prefix("    If true: throw to monkey ")
+        .ok_or(MonkeyError::ParseError())?
+        .parse::<u64>()?;
+    let false_throw = lines.next().ok_or(MonkeyError::ParseError())??
+        .strip_prefix("    If false: throw to monkey ")
+        .ok_or(MonkeyError::ParseError())?
+        .parse::<u64>()?;
+
+    // Remove empty line if exists
+    match lines.next() {
+        None => Ok(()),
+        Some(Err(e)) => Err(e),
+        Some(Ok(s)) => Ok(match s.as_str() {
+            "" => Ok(()),
+            _ => Err(MonkeyError::ParseError()),
+        }?),
+    }?;
+
+    Ok(Some(Monkey {
+        id: id,
+        items: starting_items,
+        operation: operation,
+        div_by_test: test_val,
+        true_throw: true_throw,
+        false_throw: false_throw,
+    })
+)}
+
+fn main() {
+    let file = File::open(&env::args().nth(1).unwrap()).unwrap();
+    let mut lines = io::BufReader::new(file).lines();
+    let mut monkeys: Vec<Monkey> = Vec::new();
+
+    loop {
+        match parse_monkey(&mut lines) {
+            Ok(None) => break,
+            Ok(Some(m)) => { assert!(m.id == monkeys.len() as u64); monkeys.push(m) },
+            Err(e) => eprintln!("{:?}", e),
+        }
+    }
+    let mut monkey_item_counts = vec![0; monkeys.len()];
+
+    for _round in 1..=20 {
+        for i in 0..monkeys.len() {
+            monkey_item_counts[i] += monkeys[i].items.len();
+
+            for _item in 0..monkeys[i].items.len() {
+                let old_item = monkeys[i].items.pop_front().unwrap();
+                let new_item = monkeys[i].operation.perform(old_item) / 3;
+                let new_i = if new_item % monkeys[i].div_by_test == 0 {
+                    monkeys[i].true_throw
+                } else {
+                    monkeys[i].false_throw
+                } as usize;
+                monkeys[new_i].items.push_back(new_item);
+            }
+        }
+    }
+    monkey_item_counts.sort_by(|x, y| y.cmp(x));
+    println!("{:?}", monkey_item_counts[0]*monkey_item_counts[1]);
+}
+
diff --git a/day11/test.txt b/day11/test.txt
new file mode 100644
index 0000000..30e09e5
--- /dev/null
+++ b/day11/test.txt
@@ -0,0 +1,27 @@
+Monkey 0:
+  Starting items: 79, 98
+  Operation: new = old * 19
+  Test: divisible by 23
+    If true: throw to monkey 2
+    If false: throw to monkey 3
+
+Monkey 1:
+  Starting items: 54, 65, 75, 74
+  Operation: new = old + 6
+  Test: divisible by 19
+    If true: throw to monkey 2
+    If false: throw to monkey 0
+
+Monkey 2:
+  Starting items: 79, 60, 97
+  Operation: new = old * old
+  Test: divisible by 13
+    If true: throw to monkey 1
+    If false: throw to monkey 3
+
+Monkey 3:
+  Starting items: 74
+  Operation: new = old + 3
+  Test: divisible by 17
+    If true: throw to monkey 0
+    If false: throw to monkey 1