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

public class Solution {

    static long sumOfGroup(int k1) {
        // Return the sum of the elements of the k'th group.
        long k=k1;
        long i=(k*(k-1))/2+1;
        long fe=1+(i-1)*2;
        long ans=0;
        for(int j=0;j<k;j++)
        {

            ans=ans+fe;
            fe=fe+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();
    }
}