pleas tell me where is my mistake?

var n,q,a:longint;
begin
  read(n); q:=0;
   while n>=1 do
    begin
      a:=trunc(sqrt(n));
      a:=sqr(a); inc(q);
      n:=n-a;
    end;
   write(q);
end.

Shortly, this solution (greedy - take the biggest square size possible) is incorrect. For example, let's take 12. Your solution would take 9, 1, 1, 1 - 4 pieces. But you can distribute them 4, 4, 4 - 3 pieces