#include<bits/stdc++.h>            
using namespace std;               
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)  
#define REP(i,n) for(int i=0;i<(n);i++)      
#define RREP(i,n) for (int i=(n)-1;i>=0;i--) 
                                   
#define pb push_back               
#define PII pair<int,int>          
                                   
#define VS vector<string>          
#define VI vector<int>             
#define ll long long int           
#define debug(x) cout << x << " :" <<#x << endl   
int main(void) {                   
    int n;                         
    vector<bool> p;                
    int count = 0;                 
    while(1) {                     
        count = 0;                 
        cin >> n;                  
        if(n == 0) break;          
        if(n%2 || n<4) {           
            cout << 0 << endl;     
            continue;              
        }                          
        p = vector<bool>(n,true);  
        p[0] = false;              
        int i = 3;                 
        while(i <= n) {            
            p[i] = false;          
            i += 2;                
        }                          
                                   
        i = 2;                     
        while(i <= n) {            
            if(p[i]) {             
                int j=2*(i+1) - 1; 
                while(j<=n) {      
                    p[j] = false;  
                    j += i+1;      
                }                  
            }                      
            i += 2;                
        }                          
                                   
        if(p[1] && p[n-3]) count++;                                                                                                         
        i = 2;                     
        while(i <= n/2) {          
            if(p[i] && p[n-i-2]) { 
                count++;           
            }                      
            i += 2;                
        }                          
        cout << count << endl;     
        p.clear();                 
    }                              
}