#include <iostream>#include <math.h>#include <cstring>#include <cstdio>#include <algorithm>using namespace std;const int Max=(1<<24);bool prime[Max+10];bool judge(int k){	int lim=(int)sqrt(k*1.0)+1;	for(int i=2;i<=lim;i++)	if(k%i==0) return false;	return true;}int main(){	memset(prime,true,sizeof(prime));	prime[0]=prime[1]=false;	int e=(int)sqrt(Max*1.0);	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)!=EOF){		int c=0,lim;		if(n%2==0)		lim=n/2;		else lim=n/2+1;		for(int i=2;i<=lim;i++){			if(prime[i]){				if(prime[n-i])				c++;			}		}		printf("%d\n",c);	}	return 0;}