#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <ctime>
#include <iterator>
#include <bitset>
#include <numeric>
#include <list>
#include <iomanip>
#include <cassert>
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>
using namespace std;
using ll = long long;
#define rep(i,k) for (int i = 0; i < (int)(k); i++)
#define all(cnt) begin(cnt), end(cnt)

int main() {
    int n, k;
    while (cin >> n >> k) cout << (n == 2 && k == 1 ? 0 : 1LL << (n - k)) << endl;
}