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.
        int loop = k;
        long i = 1;
        int span = 1;
        while(span != k){
            i = i + span;
            span++;
        }
        i = 2 * i -1;
        long sum = (k * (2 * i + (k-1) * 2))/2;
        return sum;
    }

    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();
    }
}