#include <bits/stdc++.h>
using namespace std;
int n,ans;
void 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: hongjiaming
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/