using System;

class URI {

static void Main(string[] args) 
{ 

        int x = Convert.ToInt32(Console.ReadLine());
        int n = Convert.ToInt32(Console.ReadLine());
        int soma, x2 = x;
        while (n < 0 || n == 0)
        {
            n = Convert.ToInt32(Console.ReadLine());
        }
        for(int i = 0; i <= n-1; i++)
        {
            x2 += i;
        }
        soma = x + x2;
        Console.WriteLine(soma);

}

}