#include <iostream>
using namespace std;
int main(void) {
	int a, b;
	cin >> a >> b;
	int cnt = 0;
	for (int i = a; i <= b; ++i) {
		double c = (a + b + i) / 3.0;
		int d = c;
		if (c == d) ++cnt;
	}
	cout << cnt << endl;
	return 0;
}