#include<iostream>
#include<vector>
#include<numeric>

int main() {
	int n, k;

	std::cin >> n >> k;

	std::vector<int> v;
	v.resize(n + 1);

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

	v[0] = 1;
	long long sum = 1;

	for (int i = 1; i < n - k + 1 ; i++) {
		sum += v[i - 1];
		v[i] = v[i - 1] * 2;
	}

	std::cout << sum << std::endl;
	
	return 0;
}