#include <bits/stdc++.h>

using namespace std;

int memo[21][21];

int solve(int n, int k) {
    if (memo[n][k]) return memo[n][k];
    if(n == 2 && k == 1) return 0;
    if (k == 1) {
        int ans = 0;
        for (int i = 1; i < n; i++) ans += solve(n - 1, i);
        memo[n][k] = ans;
        return ans;
    }
    memo[n][k] = 1 << (n - k);
    return memo[n][k];
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n, k;
    cin >> n >> k;
    cout << solve(n, k) << "\n";
    return 0;
}