#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define dunk(a) cout << (a) << endl
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll n, k;
	cin >> n >> k;

	//1-index

	if (k == 0 || k > n) {
		dunk(0);
		return 0;
	}

	int ans = n - 2;

	if (k == n - k + 1) ans++;

	dunk(ans);

	return 0;
}