Well, that's why I always define RED(x) (for reduce modulo) as ((((x) % MOD) + MOD) % MOD). Quite useful in algorithmic competitions, which often ask you for an

Well, that's why I always define RED(x) (for reduce modulo) as ((((x) % MOD) + MOD) % MOD). Quite useful in algorithmic competitions, which often ask you for answer modulo some prime.