#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,sum;
    cin >> n;
    for (int i = 1;i<=n;i++){
        if(i%2==0){
            sum -= i;
        }else{
            sum += i;
        }
    }
    cout << sum;
    return 0;
}
for 循环找规律