LL mult_mod(LL a, LL b, LL c){    a %= c; b %= c;    LL ret = 0;    LL tmp = a;    while (b){        if (b & 1){            ret += tmp;             if (ret > c) ret -= c;//直接取模慢很多        }        tmp <<= 1;        if (tmp > c) tmp -= c;        b >>= 1;    }    return ret;}LL pow_mod(LL a, LL n, LL mod){    LL ret = 1;    LL temp = a%mod;    while (n){        if (n & 1) ret = mult_mod(ret, temp, mod);        temp = mult_mod(temp, temp, mod);        n >> 1;    }    return ret;}