1 #include<stdio.h>
 2 #include<string.h>
 3 #define N 10001
 4 int prime[10001];
 5 bool check[10001];
 6 int n,i,ans,tot=0,j;
 7 
 8 void EulerPrime(){
 9     memset(check,false,sizeof(check));
10     for(i=2;i<=N;i++){
11         if(!(check[i]))prime[tot++]=i;
12         for(j=0;j<tot;j++){
13             if(i*prime[j]>N)break;
14             check[i*prime[j]]=true;
15             if(i%prime[j]==0)break;
16         }
17     }
18 }
19 
20 int main(){
21     EulerPrime();
22     while(scanf("%d",&n)!=EOF&&n!=0){
23         i=0,ans=0;
24         while(prime[i]<n/2){
25             if(check[n-prime[i]]==0)ans++;
26             i++;
27         }
28         printf("%d\n",ans);
29     }
30     return 0;
31 }