diff --git a/day10/Cargo.lock b/day10/Cargo.lock
new file mode 100644
index 0000000..5f8ea61
--- /dev/null
+++ b/day10/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day10"
+version = "0.1.0"
diff --git a/day10/Cargo.toml b/day10/Cargo.toml
new file mode 100644
index 0000000..40d2066
--- /dev/null
+++ b/day10/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day10"
+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/day10/input.txt b/day10/input.txt
new file mode 100644
index 0000000..1832939
--- /dev/null
+++ b/day10/input.txt
@@ -0,0 +1,143 @@
+noop
+noop
+addx 5
+noop
+noop
+addx 6
+addx 4
+addx -4
+addx 4
+addx -6
+addx 11
+addx -1
+addx 2
+addx 4
+addx 3
+noop
+addx 2
+addx -30
+addx 2
+addx 33
+noop
+addx -37
+noop
+noop
+noop
+addx 3
+addx 2
+addx 5
+addx 20
+addx 7
+addx -24
+addx 2
+noop
+addx 7
+addx -2
+addx -6
+addx 13
+addx 3
+addx -2
+addx 2
+noop
+addx -5
+addx 10
+addx 5
+addx -39
+addx 1
+addx 5
+noop
+addx 3
+noop
+addx -5
+addx 10
+addx -2
+addx 2
+noop
+noop
+addx 7
+noop
+noop
+noop
+noop
+addx 3
+noop
+addx 3
+addx 2
+addx 8
+addx -1
+addx -20
+addx 21
+addx -38
+addx 5
+addx 2
+noop
+noop
+noop
+addx 8
+noop
+noop
+addx -2
+addx 2
+addx -7
+addx 14
+addx 5
+noop
+noop
+noop
+addx -16
+addx 17
+addx 2
+addx -12
+addx 19
+noop
+noop
+addx -37
+noop
+noop
+noop
+addx 3
+addx 2
+addx 2
+addx 5
+addx 20
+addx -19
+addx 2
+noop
+noop
+noop
+addx 5
+addx 19
+addx -12
+addx 3
+addx -2
+addx 2
+addx -18
+addx 25
+addx -14
+addx -22
+addx 1
+noop
+noop
+noop
+addx 3
+addx 5
+addx -4
+addx 7
+addx 4
+noop
+addx 1
+noop
+noop
+addx 2
+addx -6
+addx 15
+addx -1
+addx 4
+noop
+noop
+addx 1
+addx 4
+addx -33
+noop
+addx 21
+noop
diff --git a/day10/src/main.rs b/day10/src/main.rs
new file mode 100644
index 0000000..78bcd3f
--- /dev/null
+++ b/day10/src/main.rs
@@ -0,0 +1,45 @@
+use std::env;
+use std::process;
+use std::fs::File;
+use std::io::{self, BufRead};
+
+#[derive(Debug)]
+enum Inst{
+    AddX(i64),
+    Noop,
+}
+
+#[derive(Debug)]
+struct ParseError(String);
+
+fn parse_line(line: String) -> Result<Inst, ParseError> {
+    match &line[..4] {
+        "noop" => Ok(Inst::Noop),
+        "addx" => match line[5..].parse::<i64>() {
+            Ok(operand) => Ok(Inst::AddX(operand)),
+            Err(e) => Err(ParseError(e.to_string())),
+        },
+        _ => Err(ParseError(String::from("bad instruction"))),
+    }
+}
+
+fn main() {
+    let file = File::open(&env::args().nth(1).unwrap()).unwrap();
+    let reader = io::BufReader::new(file);
+    let mut xs: Vec<i64> = vec![0, 1];
+
+    for line in reader.lines().flatten() {
+        let last_x = *xs.last().unwrap();
+        match parse_line(line) {
+            Ok(Inst::Noop) => { xs.push(last_x) },
+            Ok(Inst::AddX(x)) => { xs.push(last_x); xs.push(last_x + x) },
+            Err(e) => { eprintln!("error: {:?}", e); process::exit(1) },
+        }
+    }
+    let res: i64 = xs.iter().enumerate()
+        .skip(20).step_by(40)
+        .map(|(i, &x)| (i as i64)*x)
+        .sum();
+    println!("{:?}", res);
+}
+
diff --git a/day10/test.txt b/day10/test.txt
new file mode 100644
index 0000000..37ee8ee
--- /dev/null
+++ b/day10/test.txt
@@ -0,0 +1,146 @@
+addx 15
+addx -11
+addx 6
+addx -3
+addx 5
+addx -1
+addx -8
+addx 13
+addx 4
+noop
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx -35
+addx 1
+addx 24
+addx -19
+addx 1
+addx 16
+addx -11
+noop
+noop
+addx 21
+addx -15
+noop
+noop
+addx -3
+addx 9
+addx 1
+addx -3
+addx 8
+addx 1
+addx 5
+noop
+noop
+noop
+noop
+noop
+addx -36
+noop
+addx 1
+addx 7
+noop
+noop
+noop
+addx 2
+addx 6
+noop
+noop
+noop
+noop
+noop
+addx 1
+noop
+noop
+addx 7
+addx 1
+noop
+addx -13
+addx 13
+addx 7
+noop
+addx 1
+addx -33
+noop
+noop
+noop
+addx 2
+noop
+noop
+noop
+addx 8
+noop
+addx -1
+addx 2
+addx 1
+noop
+addx 17
+addx -9
+addx 1
+addx 1
+addx -3
+addx 11
+noop
+noop
+addx 1
+noop
+addx 1
+noop
+noop
+addx -13
+addx -19
+addx 1
+addx 3
+addx 26
+addx -30
+addx 12
+addx -1
+addx 3
+addx 1
+noop
+noop
+noop
+addx -9
+addx 18
+addx 1
+addx 2
+noop
+noop
+addx 9
+noop
+noop
+noop
+addx -1
+addx 2
+addx -37
+addx 1
+addx 3
+noop
+addx 15
+addx -21
+addx 22
+addx -6
+addx 1
+noop
+addx 2
+addx 1
+noop
+addx -10
+noop
+noop
+addx 20
+addx 1
+addx 2
+addx 2
+addx -6
+addx -11
+noop
+noop
+noop