#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; }