hdu1395 2^x mod n = 1

 1 //Accepted    228 KB    31 ms
 2 #include <cstdio>
 3 #include <cstring>
 4 __int64 n;
 5 void slove()
 6 {
 7     int ans;
 8     __int64 m;
 9     if (n%2==0 || n==1)
10     {
11         printf("2^? mod %I64d = 1\n",n);
12         return ;
13     }
14     m=1;
15     ans=0;
16     int flag=1;
17     while (flag)
18     {
19         ans++;
20         m=2*m%n;
21         if (m==1) flag=0;
22     }
23     printf("2^%d mod %I64d = 1\n",ans,n);
24 }
25 int main()
26 {
27     while (scanf("%I64d",&n)!=EOF)
28     {
29         slove();
30     }
31     return 0;
32 }