#include<iostream>
#include<cmath>
using namespace std;
int cf(int n)
{
	int r, i;
	if (n <= 1)
		return 0;
	for (i = 2; i <= int(sqrt(int(n))); i++)
		if (n%i == 0)
			break;
	if (i>int(sqrt(int(n))))
		return n;
	else
		return 0;
}
int main()
{
	int n;
	int sum = 0;
	while (cin >> n)
	{
		
		if (n == 0)
			break;
		for (int i = 0; i < n / 2; i++)
		{
			if (cf(i) && cf(n - i))
			{
				sum++;
			}
		}
		cout << sum << endl;
		sum = 0;
	}
	return 0;
}