#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<math.h>
#include<map>
#include<iomanip>
#include<queue>
#include<set>

#define rep(i,n) for(int (i) = 0; i < (n); i++)
using namespace std;
using ll = long long;
using ull = unsigned long long;

const int inf = 1e9 + 7;

int main(){ 
	int l;
	cin >> l;
	ll a = (l + 1) / 2;
	ll ans1 = a * (a - 1) / 2;
	ll b = l / 2;
	ll ans2 = b * (b - 1) / 2;
	ll ans = ans1 + ans2;
	cout << ans << endl;
	return 0;    
}