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 = 0;
        if(num == 0)
            break;
        for(i = 1; ;++ i)
        {
            for(j = i; ;++ j)
            {
                if(prime[i] + prime[j] == num)
                    ++ sum;
                if(prime[i] + prime[j] > num)
                    break;
            }
            if(prime[i] >= num/2)
            {
                break;
            }

        }
        cout<<sum<<endl;
    }
}

void give_list()
{
    int i;
    int j;
    bool prim1[M];
    memset(prim1,true,sizeof(bool)*M);
    prim1[1] = false;
    for(i = 2; i < sqrt(long double(M))+1; i ++)  
    {
        if(prim1[i])
        {
            j = 2*i;
            while(j < M)
            {
                prim1[j] = false;
                j += i;
            }
        }
    }
    j = 1;
    for(i = 2; i < M; i ++)
    {
        if(prim1[i])
        {
            prime[j] = i;
            ++ j;
        }
    }    
}