#include <iostream>
using namespace std;
int main(int argc, char* argv[])
{
	int A,B;
	cin>>A>>B;
	int aw=0;
	for (int i=A;i<=B;i++){
		if ((i+A+B)%3==0){
			aw++;
		}
	}
	cout<<aw<<endl;
	return 0;
}