import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner in = new Scanner(System.in);
		long n = in.nextInt(), a = in.nextInt(), ans;
		if (a > 1)
		{
			ans = n*a;
			for(long i = n-1; i > 0; --i)
				ans = (ans+i)*a;
		}
		else
			ans = n*(n+1)/2;
		System.out.println(ans);
	}
}