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.
        
        if(k==1)
            return 1;
        
       long start = k-1;
        
       start = start*(start+1)/2;
        
        start = start*2 + 1;
        long ans=0;
        
        for(int i=0;i<k;i++)
        {
            ans = ans+start;
            start+=2;
        }
        return ans;
        
    }

    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();
    }
}