text: #include<stdio.h>
  #define N 100000
  
  int main(void){
    int prime[N],i,j,n;
  
    for(i=2;i<N;i++)
      prime[i]=0;
  
    prime[0]=1;
    prime[1]=1;
  
    for(i=2;i*i<=N;i++){
      if(prime[i]==0){
        for(j=2*i;j<N;j+=i){
  	prime[j]=1;
        }
      }
    }
  
    while(scanf("%d",&n),n){
      int count=0;
      for(i=2;i<=n/2;i++){
        if(prime[i]==0 && prime[n-i]==0)count++;
      }
      printf("%d\n",count);
    }
    return 0;
  }
  