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 pos = (k * (k - 1)) / 2;
        long f = (2 * (pos + 1)) - 1;
        long sum = f;
        k--; 
        while(k-->0){
            f += 2;
            sum += f;
        }
        return sum;
    }

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