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

public class Solution {

    static long sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        long[] num=new long[1000000];
        long sum=0;
        long no=(((k)*(k-1))/2)+1;
        long first=1+(no-1)*2;
        for(long i=1;i<=k;i++)
        {
            sum=sum+first;
            first=first+2;
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextLong();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}