#include <bits/stdc++.h>
using namespace std;

int main()
{
int i;
int A;
int B;
int iSum;
int iCnt;

	ios::sync_with_stdio( false );
	cin.tie( 0 );

	cin >> A;
	cin >> B;

	iSum = A + B;
	iCnt = 0;
	for( i = A; i <= B; i++ )
	{
		if( ( iSum + i ) % 3 == 0 ) iCnt++;
	}

	cout << iCnt << endl;

	return 0;
}