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

int main()
{
	int A, B;
	cin >> A >> B;

	int ans = 0;
	for( int i = A; i <= B; i++ ) {
		int sum = A + B + i;
		if( sum % 3 ) continue;
		ans++;
	}

	cout << ans << endl;
}