my idea for solution
  k := 2;
  n := length(s);
  s1 := s[1];
  while true do begin
    i := 0;
    while (n - i >= k + i) and (s[k + i] = s[n - i]) do inc(i);
    if n - i <= k + i
    then begin
      write(s + s1);
      halt;
    end;
    s1 := s[k] + s1;
    inc(k);
  end;