#define  _CRT_SECURE_NO_WARNiINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include <map>
#include <fstream>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <cassert>
#include <set>
using namespace std;
#define eps 0.000000001
#define LONG_INF 10000000000000000
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
#define cycle_per_sec 2806192512
int main() {
	int a, b;
	cin >> a >> b;
	int ans = 0;
	for (int i = a; i <= b; ++i) {
		if ((a + b + i) % 3 == 0) ans++;
	}
	cout << ans << endl;
	return 0;
}