#include<bits/stdc++.h>
using namespace std;
int n,ans = 0;
void f(int s)
{
	for( int i = 1; i <= s / 2; i++)
	{
		ans++;
		f(i);
	}
}
int main(){
	cin >> n;
	f(n);
	cout << ans;
	return 0;
}

/**************************************************************
	Problem: 1307
	User: yangwanning
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/