正解

#include <iostream>
using namespace std;
typedef long long ll;
int main(){
    ll a, b, p;
    cin >> a >> b >> p;
    ll ans = 1, cheng = a, t = b;
    while(t){
        if(t % 2 == 1) ans *= cheng;
        ans %= p;
        cheng = (cheng * cheng) % p;
        t /= 2;
    }
    cout << a << "^" << b << " mod " << p << "=" << ans << endl;
    return 0;
}