#include<bits/stdc++.h>
using namespace std;
    int n,ans;
    int f(int x){
    	for(int i=1;i<=x/2;i++){
    		ans++;
    		f(i);
    	}
    }
int main(){
	cin>>n;
	f(n);
	cout<<ans;

	return 0;
}

/**************************************************************
	Problem: 1307
	User: jiangyuanfeng
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/