UVA 11287 - Pseudoprime Numbers

#include<bits/stdc++.h>
#define sf scanf
#define pf printf
#define LL long long
#define REP(i,MAX) for(int i = 0; i<MAX; i++)
#define MAX 10001
using namespace std;
bool isPrime(LL n)
{
    if(n == 1) return false;
    if(n == 2) return true;
    LL sqr = sqrt(n);

    for (LL i = 2; i <= sqr; i++)
    {
        if(n%i == 0){

            return false;
        }
    }
    return true;
}
LL big_mod(LL base, LL power, LL mod)
{
    if(power==0)    return 1;
    else if(power%2==1)
    {
        LL p1 = base % mod;
        LL p2 = (big_mod(base,power-1,mod))%mod;
        return (p1*p2)%mod;
    }
    else if(power%2==0)
    {
        LL p1 = (big_mod(base,power/2,mod))%mod;
        return (p1*p1)%mod;
    }
}
int main()
{
   ios_base::sync_with_stdio(false);
  LL p   , a;
  while(cin >> p >> a &&p &&a){
  if(isPrime(p))cout << "no\n";
  else {
    LL mod = big_mod(a,p,p);
    if(a == mod)cout << "yes\n";
    else cout << "no\n";
  }
}

 return 0;
}