using static System.Math;
using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var k = int.Parse(line[1]);
        Console.WriteLine(n >= k ? (int)Pow(2, n - k) : 0);
    }
}