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

int main() {
	int n, k, count = 1;

	std::cin >> n >> k;

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

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

	v[n] = 1;
	int sum = 1;

	for (int i = n - 1; i >= 0; i--) {
		v[i] += sum + 1;
		sum += v[i];
	}

	std::cout << std::accumulate(v.begin() + k + 1, v.end(), 1) << std::endl;
	
	return 0;
}