#include<iostream>
#include <algorithm>
#include<string>
using namespace std;

int main()
{
	int a = 0, b = 0, c = 0, d = 0, e = 0, f = 0, g = 0, h = 0;
	int n, s;
	cin >> a;
	cin >> b;
	for ( d = a; d <= b; d++)
	{
		if ((a+d+b)%3==0)
		{
			e++;
		}
	}

	cout << e << endl;


	return 0;
}