#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; i++)

int main() {
    cin.tie(nullptr);
    
    ll N;
    cin >> N;
    
    ll a = N / 2 + 1;
    ll b = N / 2;
    cout << a * (a - 1) / 2 + b * (b - 1) / 2 << '\n';
}