题解 | 牛牛学数列

#include <iostream>
#include<cmath>
using namespace std;

int main() {
    int n;
    int s =0;
    cin >> n;
     int j = 1;
    for(int i=1;i<=n;i++)
    {
        s = s +pow(-1,j-1) * j;
        j = j +1;
    }
    cout << s << endl;
}