#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int a, b;
	cin >> a >> b;

	int ans = 0;
	for (double i = a; i <= b; i++) {
		int sum = a + b + i;
		if (sum % 3 == 0) {
			ans++;
		}
	}

	cout << ans << endl;
	return 0;
}