#include<iostream>
using namespace std;
#include<cmath>
bool isprime(int n) {
	if (n == 2)return true;
	if (n % 2 == 0)return false;
	for (int i = 3; i <= sqrt(n); i += 2) if (n%i == 0)return false;
	return true;
}
int main() {
	int n; while (cin >> n, n) {
		int cnt = 0;
		for (int i = 2; i <= n / 2; i++) {
			if (isprime(i) && isprime(n - i))cnt++;
		}
		cout << cnt << endl;
	}
}