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 index = 1;
        for(int i = 0; i < k; i++){
            index += i;
        }

        long oddStart = 2 * index - 1;
        long sum = 0;
        for(int i = 0; i < k ; i++){
            sum += oddStart;
            oddStart += 2;
        }
        return  sum;
    }

    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();
    }
}