题解 | #小乐乐求和#

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();
        sum.sumz(n);
    }
}
class Sum {
    public void sumz(int n) {
        long sum = 0;
        for(int i = n; i >= 1; i--) {
            sum += i;
        }
        System.out.println(sum);
    }
}