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

int main()
{
int A;
int B;
int C;

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

	cin >> A;
	cin >> B;

	C = B - A;

	cout << ( A + 2 * B ) / 3 - ( 2 * A + B - 1 ) / 3 << endl;

	return 0;
}