import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(int k) {
        long kMinusOne = k-1;
        long whichNumbersWasBefore = ((1+kMinusOne)*kMinusOne);
        long firstElement = whichNumbersWasBefore+1;
        long[] numbers = new long[k];
        for(int i = 0; i<k; i++){
            long elementOfI = firstElement + (i*2);
            numbers[i] = elementOfI;
        }
        long result = 0;
        for (long number:numbers) {
           result+=number;
        }
        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();
    }
}