import java.io.*;
    import java.util.*;

    public class Solution {

        static long sumOfGroup(long k) {
            long first = k*(k-1) + 1;
            long result = 0;
            for(int i = 0; i < k; i++) {
//                System.out.println((first + 2*i));
                result+=first +2*i;
            }
            return result;
        }


        public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            int k = in.nextInt();
            long answer = sumOfGroup(k);
            System.out.println(answer);
            in.close();
        }
    }