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 init = (n*n - n) / 2 + 1;
        long last = (n*n + n) / 2;
        long ans = n * (2*init-1 + 2*last-1) / 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();
    }
}