题解 | 牛牛学数列

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int sum = 0;
        for (int i=1;i<=a;i++){
            sum+=i*(i%2==1?1:-1);
        }
        System.out.println(sum);
    }

}