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 k1=k;
        long odd=((k1-1)*(k1-1+1)/(long)2)*(long)2+(long)1;
        long sum=0;
        sum+=odd;
        for(int i=1;i<k;i++){
            odd=odd+2;
            sum+=odd;
            }
        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();
    }
}