#include<bits/stdc++.h>
using namespace std;
int main()
{
	unsigned long long x,k,a,b,c;
	cin>>x>>k;
	a=x%3;
	a=3-a;
	k-=a;
	x=(x+a)/3;
	b=k%3;
	c=(k-b)/3;
	x=x+b+c;
	cout<<x;
	return 0;
}