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

public class Solution {

    static long sumOfGroup(int k) {
        long a=0;
        long diff = 1;
        long sum=0;
                    
        while(diff<k)
        {
            a=a+diff;
            diff++;
        }
        //System.out.println(a);
        for(long i=a;i<a+k;i++)
            sum+=i;
        return (2*sum + k);
    }

    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();
    }
}