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 sum=0,n;
        long a=0;
        for(long i=k-1;i>=1;i--){
            sum+=i;
        }
        long x=(2*sum)+1;
        for(long i=0;i<k;i++){
            a+=x;
            x=x+2;
        }
        return a;
    }

    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();
    }
}