题解 | #牛牛学数列#

import java.util.*;

public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
           System.out.println(sum(n));
    }
    
    public static int sum(int n){
        int sum = 0;
        int c = - 1;
       for(int i = 1; i <= n; i++){
           c *= -1;
          sum += i * c;
       }
        return sum;
    }
}