Problem with ABC Pascal

[AlanJohn]

So recently I have been programming in pascal because I can, and I have encountered a serious problem with my compiler ABC pascal. Basically, it won't write anything in the output.txt file. Here's the code, but the problem is not in it (as far as I know):

program strings;
 
var
  U, V, S: string;
  f1, f2: text;
 
begin
  assign(f1, 'input.txt');
  assign(f2, 'output.txt');
  reset(f1);
  rewrite(f2);
  readln(f1, u);
  readln(f1, v);
  S:= u + v;
  writeln(f2, S);
  close(f1);
  close(f2);
end.

And here is input.txt:

alan
john

So, what may be the problem?