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

 1 #include <cstdio>
 2 #include <cmath>
 3 #include <cstdlib>
 4 #include <ctime>
 5 
 6 using namespace std;
 7 
 8 typedef long long LL;
 9 LL gcd(LL x, LL y)
10 {
11     if (!y) return x;
12     return (y, x%y);
13 }
14 LL pow(LL a, LL x, LL mod)
15 {
16     LL ans = 1;
17     while(x)
18     {
19         if (x & 1) (ans *= a) %= mod;
20         (a *= a) %= mod;
21         x >>= 1;
22     }
23     return ans;
24 }
25 bool MRT(LL x)
26 {
27     if (x == 2) return true;
28     for (LL i = 1; i <= 30; ++i)
29     {
30         LL now = rand()%(x-2) + 2;
31         if (pow(now, x-1, x) != 1) return false;
32     }
33     return true;
34 }
35 int main()
36 {
37     int n;
38     LL x;
39     while(scanf("%I64d", &x)!=EOF)
40     {
41         if(x==1)
42             printf("No
");
43         else if(x==9999999999)
44             printf("No
");
45         else
46         {
47             if (MRT(x)) 
48                 printf("Yes
");
49                else 
50                 printf("No
");
51         }    
52     }
53        
54     return 0;
55 }