#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <map>
#include <cmath>
#include <queue>
#include <utility>
#include <functional>
#include <deque>
#include <cctype>
#include <stack>
#include <bitset>
#include <set>

using namespace std;
using ll = long long;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

const ll MOD = 1e9 + 7;
const ll INF = 1 << 30;
const ll INF2 = 9e18;
const double INF3 = 9e14;
const int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
const int tx[8] = { -1,0,1,-1,1,-1,0,1 }, ty[8] = { -1,-1,-1,0,0,1,1,1 };
#define ALL(x) (x).begin(),(x).end()
#define pb push_back
#define fr first
#define sc second




int main() {
	int a, b, ans = 0;
	cin >> a >> b;
	for (int i = a;i <= b;i++) {
		if ((a + b + i) % 3 == 0)ans++;
	}
	cout << ans << endl;
	return 0;
}