#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <numeric>
#include <optional>
#include <vector>

using namespace std;

int main() {
    int32_t l;
    cin >> l;
    int64_t t = l / 2, s = t - 1;
    cout << t * (t + 1) / 2 + s * (s + 1) / 2 << endl;
    return 0;
}