#include <fstream>
#include <iostream>

int main() {

	//std::ifstream inf("Text.txt");	std::cin.rdbuf(inf.rdbuf());

	int A, B;
	std::cin >> A >> B;

	int ans = 0;
	for (int i = A; i <= B; i++) {
		if ((A + B + i) % 3 == 0) {
			ans++;
		}
	}

	std::cout << ans << std::endl;

	return 0;
}