java等差数列求和

import java.util.Scanner;
public class a17 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("输入一个数");
         int n = sc.nextInt();
         int Sn;
         int an = n;
         Sn = (1+an)*n/2;   //a1 = 1
         System.out.println(Sn);
    }
}