function f(n: integer): integer;
var
  r, res, pos: integer;
begin
  r:= 0;
  pos:= 0;
  res:= n;
  while (n div 10) <> 0 do
  begin
    if (n mod 10 = 5) then
    begin
      res:= (n - 5) * trunc(exp(pos * ln(10))) div 10 + r;
      break;
    end
    else if (n mod 10 = 0) then
    begin
      res:= n * trunc(exp(pos * ln(10))) div 10 + r;;
      break;
    end;
    r:= r + ((n mod 10) * trunc(exp(pos * ln(10))));
    n:= n div 10;
    inc(pos);
  end;
  if (n mod 10) = 5 then
    res:= res mod trunc(exp(pos * ln(10)));
  f:= res;
end;