using System;
using System.Collections.Generic;
using System.Linq;

class Program {
    static string ReadLine() { return Console.ReadLine(); }
    static int ReadInt() { return int.Parse(ReadLine()); }
    static int[] ReadInts() { return ReadLine().Split().Select(int.Parse).ToArray(); }
    static string[] ReadStrings() { return ReadLine().Split(); }

/*
    static long Combination(int n, int r) {
        long num = 1;
        long den = 1;
        for (int i = 0; i < r; i++) {
            num *= n - i;
            den *= r - i;
        }
        return num / den;
    }

    static long Calc(int n, int k) {
        if (k == 1 && n == 2) return 0;

        long sum = 0;
        int p = n - k;
        for (int i = 0; i <= p; i++) {
            sum += Combination(p, i);
        }
        return sum;
    }
*/
    static int Calc(int n, int k) {
        int ans = 0;
        var xs = new bool[n];
        for (int i = 1; i < (1 << n); i++) {
            int max = 0;
            int min = int.MaxValue;
            bool ng = false;
            for (int j = 0; j < n; j++) {
                if ((i & (1 << j)) != 0) {
                    if (j < k) { // 先頭は k なのでスキップ
                        ng = true;
                        break;
                    }
                    xs[j] = true;
                    max = j;
                }
                else {
                    xs[j] = false;
                    min = Math.Min(min, j);
                }
            }

            if (ng) continue;

            if (xs[k] && max > min) {
                ans++;
            }
        }
        return ans;
    }

    static void Main() {
        var xs = ReadInts();
        int n = xs[0], k = xs[1];
        Console.WriteLine(Calc(n, k-1));
    }
}