#include<iostream>
#include<vector>
using namespace std;
vector<int> table;
void priTable();
int primeNumber(int);
int main()
{
int n;
priTable();
while(cin>>n && n!=0){
int count=0;
for(vector<int>::iterator it=table.begin();(*it)<n/2;++it){
int temp=n-(*it);
if(primeNumber(temp)){
count++;
}
}
cout<<count<<endl;
}
return 0;
}
void priTable(){
for(int i=2;i<10001;++i){
if(primeNumber(i))table.push_back(i);
}
}
int primeNumber(const int num){
for(int i=2;i*i<=num;++i){
if(num%i == 0)return 0;
}
return 1;
}