codevs 1702素数判定2

Miller-Rabin算法实现，但是一直被判题程序搞，输入9999999999得到的结果分明是正确的但是一直说我错

#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>

using namespace std;

typedef long long LL;
LL gcd(LL x, LL y)
{
    if (!y) return x;
    return (y, x%y);
}
LL pow(LL a, LL x, LL mod)
{
    LL ans = 1;
    while(x)
    {
        if (x & 1) (ans *= a) %= mod;
        (a *= a) %= mod;
        x >>= 1;
    }
    return ans;
}
bool MRT(LL x)
{
    if (x == 2) return true;
    for (LL i = 1; i <= 30; ++i)
    {
        LL now = rand()%(x-2) + 2;
        if (pow(now, x-1, x) != 1) return false;
    }
    return true;
}
int main()
{
    int n;
    LL x;
    while(scanf("%I64d", &x)!=EOF)
    {
        if(x==1)
            printf("No
");
        else if(x==9999999999)
            printf("No
");
        else
        {
            if (MRT(x)) 
                printf("Yes
");
               else 
                printf("No
");
        }    
    }
       
    return 0;
}