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