#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int main() {
    int n;
    cin >> n;
    int t = 1, sum = 0;
    for (int i = 1 ; i <= n ; i ++) {
        sum += i * t;
        t = -t;
    }
    cout << sum << endl;


    return 0;
}
// 64 位输出请用 printf("%lld")