POJ 3641 Pseudoprime numbers

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;

long long mod_exp(long long a, long long b, long long c)
{
    long long res, t;
    res = 1 % c;
    t = a % c;
    while (b)
    {
        if (b & 1) res = res * t % c;
        t = t * t % c;
        b >>= 1;
    }
    return res;
}

bool prime(long long x)
{
    for(long long i=2;i*i<=x;i++)
        if(x%i==0) return 0;
    return 1;
}

int main()
{
    long long p,a;
    while(~scanf("%lld%lld",&p,&a))
    {
        if(p==0&&a==0) break;
        if(prime(p)) printf("no\n");
        else if(mod_exp(a,p,p)==a) printf("yes\n");
        else printf("no\n");
    }
    return 0;
}