#include <iostream>

using lint = long long;

void solve() {
    int n, k;
    std::cin >> n >> k;

    if (n == 2 && k == 1) {
        std::cout << 0 << std::endl;
        return;
    }

    int ans = (1 << (n - k));
    if (k == 1) --ans;
    std::cout << ans << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}