#include <iostream>
using namespace std;

inline long long ap_sum(long long a, long long b) {
    return (a + b) * (b - a + 1) / 2;
}

int main() {
    int L;
    cin >> L;
    cout << ap_sum(1, (L-3)/2+1) + (L>=5? ap_sum(1, (L-5)/2+1): 0) << endl;

    return 0;
}