#include <iostream>

using namespace std;

int main() {
	int a, b;
	cin >> a >> b;

	int ans = 0;
	for (int i = a; i <= b; i++) {
		int sum = a + i + b;
		if (sum % 3 == 0) {
			ans++;
		}
	}

	cout << ans << endl;
	return 0;
}