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

    static long sumOfGroup(int k) {
        long i,num=1,add=2;
        for(i=1;i<k;i++){
            num+=add;
            add+=2;
        }
        long sum=num;
        for(i=0;i<k-1;i++){
            num+=2;
            sum+=num;
        }
        return sum; 
    }

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