//No.682 Average
#include<iostream>
using namespace std;
int main()
{
	int A, B;
	cin >> A >> B;
	int cnt = 0;
	for (int i = A; A <= B; A++) {
		if ((A + B + i) % 3 == 0) {
			cnt++;
		}
	}
	cout << cnt;
	return 0;
}