#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

int fun(int n){
    int k = 1;
    int sum = 0;
    for (int i = 1; i <= n; i++){
        sum += k * i;
        k *= -1;
    }
    return sum;
}

int main()
{
    int n = 50;
    int sum = fun(n);
    printf("%d", sum);
    return 0;
}