#include<iostream>
#include<cmath>
using namespace std;
bool pri(int k)
{
	int i;
	for(i=2;i<=sqrt(k);i++)
		if(k%i==0)
			break;
		if(i>sqrt(k))
			return 1;
		return 0;
}

int main()
{
	int n;
	while(cin>>n,n)
	{
		int count=0;
		for(int k=2;k<n/2;k++)
			if(pri(k)&&pri(n-k))
				count++;
			cout<<count<<endl;
	}
	return 0;
}