提示:不需要递归/递推

#include<iostream>
using namespace std;
/*
int f(long long n){
    if (n == 1) return -1;
    if (n%2 == 1) return f(n-1)-n;
    return f(n-1)+n;
}
*/
int main(){
    long long n;
    cin >> n;
    /*cout << f(n) << endl;
    long long s=0;
    for (int i=1;i<=n;i++){
        if (i%2 == 1) s-=i;
        else s+=i;
    }
    */
    long long s;
    if (n%2==0) s=n/2;
    else s=n/2-n;
    cout << s << endl;
    return 0;
}