#include<bits/stdc++.h>
using  namespace  std;
int n,c=0,i=2;
int x(int i)
{
    for(int j=2;j*j<=i;j++)
    {
        int b=1;
        if(i%j==0)
        {b=0;return 0;}
        
    }
    return 1;
    
}
int  main()
{
    cin>>n;
    while(i<=n/2)
    {
    if(x(i)&&x(n-i))c++;
    if(i>=3)i+=2;
    else i++;
    }
    cout<<c;
    return 0;
}