#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>#include <cmath>using namespace std;const int Max=10050;bool prime[Max+10];int main(){	memset(prime,true,sizeof(prime));	prime[0]=prime[1]=false;	int e=(int)sqrt(1.0*Max);	for(int i=2;i<=e;i++){		if(prime[i]){			for(int j=i+i;j<=Max;j+=i)			prime[j]=false;		}	}	int n;	while(scanf("%d",&n),n){		int c=0; 		int lim;		if((n%2)==0)		lim=n/2;		else lim=n/2+1;		for(int i=2;i<=lim;i++)		if(prime[i]&&prime[n-i]){			if(i!=n-i)			c++;		}		printf("%d\n",c);	}	return 0;}