#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<iomanip>
#include<queue>
using namespace std;
typedef long long int lint;
int main() {
	double A, B;
	cin >> A >> B;
	int cnt = 0;
	for (int ia = A; ia <= B; ia++) {
		if (int((A + B + ia) / 3) - (A + B + ia) / 3==0) {
			cnt++;
		}
	}
	cout << cnt << endl;
}