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.
        int groupLastNumber = 0;
        int c=1;
        for(int i=1; i<=k; i++){
                //calculate the sum of numbers till k - it will give us the last number in the group we want
            groupLastNumber +=i;
            }
        //the group of numbers array
        int[] group = new int[groupLastNumber];
        int last =0;
        while(c<=k){
       
           last= (last + (2*groupLastNumber - 1)) -2;
       
        c++;
        }
        return last;
    }

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