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)

/*
 * 17-2-18_ARC069_A.cpp
 *
 *  Created on: 2017/02/18
 *      Author: ryoma
 */

#include<iostream>
#include<algorithm>

using namespace std;

long long N,M;
long long ans;
int main(){
	cin >> N >>M;
	ans = min(N,M/2);
	N -= ans;
	M -= 2*ans;
	ans += M/4;
	cout << ans << endl;
	return 0;
}