#include<iostream>
using namespace std;
int main() {
	unsigned long long a , b;
	cin >> a >> b;
//	if ( a <= 1000 || b <= 1000 ) return 0;
	if ( b < a ) {
		unsigned long long sw = a;
		a = b;
		b = sw;
	}//b > a
	if ( b >= 2 * a ) {
		cout << 2 * a << endl;
		return 0;
	}
	unsigned long long k = a + b;
	k *= 2;
	k /= 3;
	if ( k % 2 == 1 ) --k;
	printf ( "%d\n" , k );
	return 0;
}
