#include <iostream>
#include <sstream>

using namespace std;

int main(int argc, char *argv[])
{
	int N, K;
	cin >> N >> K;
	int ans = 0;
	if (K == 1) {
		ans = (N * (N - 1)) / 2 - 1;
	} else {
		ans = N - 1;
	}
	cout << ans << endl;
	return 0;
}