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 s = ((k-1)*k)/2;
      int sum =0;
        int j =0;
        int o = 0;
        for(int i=1 ; i<(2*s) ;i++)
        {
            if(i%2!=0)
            {
                j = i+2;
            }
        }
        
              sum = ((k)*((2*j)+((k-1)*2)))/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();
    }
}