题解 | #牛牛学数列4#

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        Sum sum = new Sum();
        System.out.println(sum.sumZs(n));
    }
}
class Sum {
    public int sumZs(int n) {
        int sum = 0;
        if(n > 0) {
            for(int i = 1; i <= n; i++) {
                sum += i;
            }
            return sum + sumZs(n - 1);
        } else {
            return 0;
        }
    }
}