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

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

    static void Main(String[] args) {
        int k = Convert.ToInt32(Console.ReadLine());
        long answer = sumOfGroup(k);
        Console.WriteLine(answer);
    }
}