package v006;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.util.ArrayList;

import java.util.StringTokenizer;

public class GoldbachConjectureII_UVa686{

static ArrayList<Integer> primes;

static boolean[] notPrime;

public static void sieve(int N) {

notPrime = new boolean[N+1];

notPrime[0] = notPrime[1] = true;

primes = new ArrayList<Integer>();

for (int i = 2; i <= N; i++)

if (!notPrime[i])

{

primes.add(i);

for (int j = i * i; j <= N; j += i)

notPrime[j] = true;

}

}

public static void main(String[] args) throws IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

StringBuilder sb = new StringBuilder();

while(true)

{

primes = new ArrayList<Integer>();

String line = br.readLine();

StringTokenizer st = new StringTokenizer(line);

int N = Integer.parseInt(st.nextToken());

if(N==0)

break;

sieve(N);

int count = 0;

int i = 0;

while(true)

{

int prime = primes.get(i++);

if(prime * 2 > N)

break;

int other = N - prime;

if(!notPrime[other])

count++;

}

sb.append(count+"\n");

}

System.out.print(sb);

}

}