using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {

    static long sumOfGroup(long k)
        {
            // Return the sum of the elements of the k'th group.
            long first = (k - 1) * (k) / 2;
            long start = (2*first) - 1 + 2;
            long sum = start;
            long next = 0;
            for(int i = 1; i < k; ++i)
            {
                next = start + 2;
                sum += next;
                start = next;
            }
            return sum;
        }

        static void Main(String[] args)
        {
            long k = Convert.ToInt64(Console.ReadLine());
            long answer = sumOfGroup(k);
            Console.WriteLine(answer);
            Console.Read();
        }
}