WhatsInAName

int64_t modPow(int64_t a, int64_t x) {
    int64_t res = 1;
    while(x > 0) {
        if( x % 2 != 0) {
            res = ModM(res * a);
        }
        a = ModM(a*a);  //right here

        x /= 2;
    }
    return res;
}