package aoj.contest1399;

import java.util.Scanner;
public class H_Goldbach {
   public static void main(String[] args){
       Scanner cin=new Scanner(System.in);
       int n=cin.nextInt(),sum=0;
       for(int i=n/2;i>=2;i--)
           if(prime(i)&& prime(n-i)) sum++;
       System.out.println(sum);
       cin.close();
   }
 
private static boolean prime(int n) {
    for(int i=2;i*i<=n;i++)
        if(n%i==0)return false;
    return true;
}
}