#include <bits/stdc++.h>

using namespace std;

int main() {
    long long l, ct = 0;
    
    cin >> l;
    
    ct = l / 2;
    
    for (long long i = 1; i < l/2; i++) {
        ct += i * 2;
    }
    
    cout << setprecision(20) << ct << endl;
    
    return 0;
}