using namespace std;
int s[110];
int main() {
	int n, m, res = 0,cnt=1;
	cin >> n >> m;
	int k = m / 2;
	if (n <= k) { cout << 0; 
	return 0;
	}
	else {
		s[1] = 1;
		for (int i = 1; i <= m - 2; i+=2) {
			if (cnt < n) {
				s[i + 2] = 1;
				cnt++;
			}
		}
		if (cnt < n) {
			for (int i = 2; i <= m - 3; i+=2) {
				if (cnt < n) {
					s[i + 2] = 1;
					cnt++;
				}
			}
		}
	}
	for (int i = 2; i <= m - 1; i++) {
		if (s[i] == 1) {
			if (s[i - 1] == 1) res++;
			if (s[i + 1] == 1) res++;
		}
	}
	if (s[m] == 1) res++;
	if (s[2] == 1) res++;
	if (s[m - 1] == 1&&s[m]==1) res++;
	if (s[1] == 1&&s[m]==1) res++;
	cout << res;
	return 0;
}