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 temp = k;
        long sP = ((temp-1)*(temp)/2)+1;
        long result = 0;
        //System.out.println(sP);
        for(long i=sP;i<sP+temp;i++){
            
            result+= i+(i-1);
          //  System.out.println(result);
        }
        return result;
    }

    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();
    }
}