#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;



int main() {
	int i, j, k;
	double a, b;

	cin >> a >> b;

	int cnt = 0;


	for (double i = a; i <= b; i++) {
		double num = (a + b + i) / 3.0;
		if (fmod(num, 1) == 0)cnt++;
	}

	cout << cnt << endl;







	getchar();
	getchar();
	return 0;
}