% :- use_module(library(readln)).
% :- initialization(start, main).

start :-
    input(Input),
    findall(P, (member(L, Input), predict(L, P)), Ps),
    sum_list(Ps, Answer),
    writef('Answer=%t\n', [Answer]).

predict(L, 0) :- maplist(=:=(0), L), !.
predict(L, X) :-
    foldl([Li1, Li2, C, D]>>(Li2 is Li1 - C, D = Li1), L, [_ | NewL], 0, _),
    predict(NewL, SubX),
    last(L, LastL),
    X is SubX + LastL.

% this does not work very lame readln cannot handle negative numbers
% input(Lines) :-
%     readln(LineTmp),
%     (   (last(LineTmp, end_of_file); LineTmp = [])
%     ->  Lines = []
%     ;   Line = LineTmp,
%         input(CdrLine),
%         Lines = [Line | CdrLine]
%     ).