long long也开了，似乎找不到什么问题

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll mi(ll a,ll b,ll p)
{
	if(b==0) return 1;
	if(b==1) return a;
	ll t=(mi(a,b/2,p)%p+p)%p;
	if(b%2==0) return (t*t+p)%p;
	else return ((t*t*a)p)%p;
}
int main()
{
	ll a,b,p;
	cin>>a>>b>>p;
	cout<<a<<"^"<<b<<" mod "<<p<<"="<<mi(a,b,p);
	return 0;
}