#include <bits/stdc++.h>
using namespace std;
int main() {
  unsigned long long n;
  while (scanf("%llu", &n) != EOF) {
    unsigned long long ans;
    if (n % 2 == 0) {
      ans = n / 2;
      printf("%llu\n", ans);
    } else {
      ans = n - (n - 1) / 2;
      printf("-%llu\n", ans);
    }
  }
}
