import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Scanner;
public class Solution {

    public static void main(String[] args) {
        // write your code here

        Scanner scanner = new Scanner(System.in);
        int k = scanner.nextInt();
        long a =0;
        long b = 0;
        for(int i=1;i<=k;i++){
            if(k==1){
                System.out.println(1);
                return;
            }else{
                b=a;
                a=a+i;
            }
        }
        System.out.println(a*a - b*b);
    }


}