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 n = k;
        long ct = n*(n-1)/2;
        long first = 1 + (ct)*2; 
        long sum = 0;
        for(long i = 0; i < k;i++ ){
            sum = sum + first;
            first += 2;
        }
        // Return the sum of the elements of the k'th group.
        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();
    }
}