import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(long k) {
        long x = (k*(k-1))/2;
        x += 1;
        long a = 1 +(x-1)*2;
        long sum = (((a)+(k-1))*k);
        //System.out.println(a+" "+sum);
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextLong();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}