#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
const int64_t mod = 1e9 + 7;

int main() {
	int A, B;
	cin >> A >> B;

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

	cout << cnt << endl;
}