C++ 代码

#include<iostream>
using namespace std;

typedef unsigned long long ULL;

int main()
{
    ULL a,b,p;
    cin >> a >> b >> p;
    ULL res = 0;
    while(b)
    {
        if(b & 1) res = (res + a) % p;
        a = a * 2 % p;
        b >>= 1;
    }
    cout << res << endl;
    return 0;
}