POJ 2909

 #include<iostream>
 #include<stdio.h>
 #define M 35000
 #include<math.h>
 #define N 3800
 using namespace std;

 int prime [N];
 void give_list();
 int main()
 {
     //freopen("acm.acm","r",stdin);
     int i;
     int j;
     int num;
     int sum;
     give_list();
     while(cin>>num)
     {
         sum = ;
         if(num == )
             break;
         for(i = ; ;++ i)
         {
             for(j = i; ;++ j)
             {
                 if(prime[i] + prime[j] == num)
                     ++ sum;
                 if(prime[i] + prime[j] > num)
                     break;
             }
             if(prime[i] >= num/)
             {
                 break;
             }

         }
         cout<<sum<<endl;
     }
 }

 void give_list()
 {
     int i;
     int j;
     bool prim1[M];
     memset(prim1,true,sizeof(bool)*M);
     prim1[] = false;
     for(i = ; i < sqrt(long double(M))+; i ++)
     {
         if(prim1[i])
         {
             j = *i;
             while(j < M)
             {
                 prim1[j] = false;
                 j += i;
             }
         }
     }
     j = ;
     for(i = ; i < M; i ++)
     {
         if(prim1[i])
         {
             prime[j] = i;
             ++ j;
         }
     }
 }