#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i;
	cin>>n;
	if(n%2==0){
	    i=n/2;
	    cout<<i;
	
	}
	return 0;
}
/**************************************************************
	Problem: 1244
	User: linyuhang
	Language: C++
	Result: Wrong Answer
****************************************************************/