题解 | 等差数列

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextInt()) {
            int a = sc.nextInt();
            int b = 2;
            int c = b;
            for (int i =0; i <a-1; i++) {
                b+=3;
                c+=b;
            }
            System.out.println(c);
        }
    }
}