#include <bits/stdc++.h>
#define For(i, a, b) for(long long i = a; i < b; i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(long long i = a; i >= b; i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
using namespace std;

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

int main() {
    lint l;
    cin >> l;
    lint x = (l - 1) / 2;
    lint a = (1 + x) * x / 2, b = (1 + (x - 1)) * (x - 1) / 2;
    cout << a + b << endl;
}