#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> Pr;

ll L;

int main()
{
	cin >> L;
	ll b = L / 2;
	ll a = 0;
	if (L % 2 != 0)a = b + 1;
	else a = b;

	cout << (a-1)*(a-1 + 1) / 2 + (b-1)*(b-1 + 1) / 2 << endl;
	return 0;
}