#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

//#include<bits/stdc++.h>


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;
}