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

#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;
}

#include<iostream>
using namespace std;
int sushu(int n){
    if(n<=1)return 0;
    if(n==2)return 1;
    if(n%2==0)return 0; 
    for(int i=3;i*i<=n;i+=2){
        if(n%i==0){
            return 0;
        }
    }
    return 1;
}
int main (){
    int n,sum=0;
    cin>>n;
    for(int i=2;i<=n/2;i++){
        if(sushu(i)&&sushu(n-i)){
            sum++;
        }
    }
    cout<<sum<<endl;
    return 0;
}

#include<iostream>
using namespace std;
int sushu(int n){
if(n<=1)return 0;
if(n==2)return 1;
if(n%2==0)return 0;
for(int i=3;i*i<=n;i+=2){
if(n%i==0){
return 0;
}
}
return 1;
}
int main (){
int n,sum=0;
cin>>n;
for(int i=2;i<=n/2;i++){
if(sushu(i)&&sushu(n-i)){
sum++;
}
}
cout<<sum<<endl;
return 0;
}