debug = false;

int tower(int to_move, string source, string dest, string temp)
{
  if (to_move > 0) {
    if (debug) {
      print("move a disc from ", source, " to ", dest, "\n");
    }
    a = tower(to_move - 1, source, temp, dest);
    b = tower(to_move - 1, temp, dest, source);
    return a + b + 1;
  } else {
    return 0;
  }
}

for (i = 1; i < 10; i++) {
  moves = tower(i, "left", "right", "center");

  if (moves != 2 ** i - 1) exit(1);
}