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

public class Solution {

    static long sumOfGroup(int k) {
        int j=0;
        long sum=0;
        long odd=0;
        for(j=1;j<k;j++){
           odd=odd+j;
        }
        odd=odd*2+1;
        for(j=0;j<k;j++){
            sum+=odd;
            odd+=2;
        }
        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();
    }
}