Problem:
Score : 300 points

Problem Statement

Snuke loves puzzles.

Today, he is working on a puzzle using S- and c-shaped pieces.
In this puzzle, you can combine two c-shaped pieces into one S-shaped piece, as shown in the figure below:

Snuke decided to create as many Scc groups as possible by putting together one S-shaped piece and two c-shaped pieces.

Find the maximum number of Scc groups that can be created when Snuke has N S-shaped pieces and M c-shaped pieces.

Constraints

1 ≤ N,M ≤ 10^{12}

Input

The input is given from Standard Input in the following format:

N M

Output

Print the answer.

Sample Input 1

1 6

Sample Output 1

2

Two Scc groups can be created as follows:

Combine two c-shaped pieces into one S-shaped piece

Create two Scc groups, each from one S-shaped piece and two c-shaped pieces

Sample Input 2

12345 678901

Sample Output 2

175897

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>

#define lli long long int
#define REP(i,n) for(int i=0;i<n;i++)
#define DEBUG 0

using namespace std;

lli min(lli a,lli b){
	return a <= b ? a : b;
}

int main(){

	lli a,b;
	cin>>a>>b;

	lli ans = min(a,b/2);

	if(DEBUG)cout<<ans<<endl;

	a -= ans;
	b -= ans*2;

	ans += b/4;

	cout<<ans<<endl;

	return 0;
}