#include <iostream>

using namespace std;

long long sum_even, sum_odd, n;

int main() {
    sum_even = 0;
    sum_odd = 0;
    cin >> n;

    for (int i = 1 ; i <= n ; i++) {
        if (i % 2 == 0) {
            sum_even += i;
        } else {
            sum_odd += i;
        }
    }
    cout << sum_odd - sum_even << endl;
    return 0;
}