program vaneck;
    eck := [0];

    loop for i in [1..999] do
        prev := eck(..#eck-1);
        eck(i+1) := i - (max/[j : e=prev(j) | e=eck(i)] ? i);
    end loop;

    print(eck(1..10));
    print(eck(991..1000));
end program;