#include <cstdio>
#include <vector>
using namespace std;

bool isprime[50010];
int ans[50010];

int main(){
	for(int i = 2; i <= 50000; ++i){
		isprime[i] = true;
	}
	for(int i = 2; i < 300; ++i){
		if(isprime[i]){
			for(int j = i * i; j <= 50000; j += i){
				isprime[j] = false;
			}
		}
	}

	vector<int> primes;
	for(int i = 2; i <= 50000; ++i){
		if(isprime[i]) primes.push_back(i);
	}

	for(int i = 0; primes[i] <= 25000; ++i){
		for(int j = i; primes[i] + primes[j] <= 50000; ++j){
			++ans[primes[i] + primes[j]];
		}
	}

	int n;
	while(scanf("%d", &n), n){
		printf("%d\n", ans[n]);
	}
}