#include <iostream>
using namespace std;

int main() {
	int a, b;
	cin >> a >> b;
	
	int x = (2 * a + b) % 3;
	if (x != 0) x = 3 - x;
	
	cout << (b - (a + x) + 3) / 3 << endl;
	return 0;
}