#include <iostream>

using namespace std;
using ll = long long;
using ull = unsigned long long;

int main () {
    ll N; cin >> N;
    ll M = N + 1;
    if (N % 2 == 0) {
        N /= 2;
    }
    else {
        M /= 2;
    }

    ull ans = 1ULL * N * M;
    cout << ans << "\n";
}