import java.io.*; import java.util.*; import java.text.*; import java.math.*; import java.util.regex.*; public class Solution { static long sumOfGroup(int k) { // Return the sum of the elements of the k'th group. long minus = k - 1; long odd = (minus *(1 + minus))/2; long start = (2 * odd) + 1; long d = 2 * k; long all = (d * (start + (start + d - 1)))/2; long ans = ((all - k)/2); return ans; } 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(); } }