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.
        // Return the sum of the elements of the k'th group.
    // group 1 1 elem
    // group k starts with the (1 + 2 + .. + (k-1))
    long lo = (long)k * (k-1)  + 1; 
    // it has k element
    long hi = lo + 2 * (k - 1);
    return (lo + hi) * k / 2;
    }

    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();
    }
}