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