题解 | #等差数列#

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            int last = 2 + (n - 1) * 3;
            System.out.println(n * (2 + last) / 2);
        }
    }
}