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