#include <iostream>

using namespace std;

int main(){
	long int n, k;
	cin >> n >> k;
	if (k == 0 || k > n) cout << 0 << endl;
	else{
		if (n == k) cout << n - (n / k) -1 << endl;
		else	cout << n-(n/k) << endl;
	}

}