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 scanner = new Scanner(System.in);
        scanner.useDelimiter("\n");

        while (scanner.hasNextInt()) {
            int i = scanner.nextInt();
            int res = 2;
            int result = res;
            for (int j = 1; j < i; j++) {
                res+=3;
                result+=res;
            }
            System.out.println(result);
        }
    }
}