#include <iostream>
#include <vector>
using namespace std;

int main()
{
	int n, d;
	cin >> n >> d;

	if (n == d) {
		cout << 0 << endl;
	}
	if (!(n%d)) {
		cout << n / d -1 << endl;
	}
	else {
		cout << n - 1 << endl;
	}

	return 0;
}