_ check_assoc(op, a, b, c) {
  return op(op(a, b), c) == op(a, op(b, c));
}

int main(int x, int y, int z) {
  return check_assoc(_+_, x, y, z);
}

{-
    method_id | in         | out
TESTCASE | 0  | 2 3 9      | -1
TESTCASE | 0  | 11 22 44   | -1
TESTCASE | 0  | -1 -10 -20 | -1
-}