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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
  fscanf(STDIN,"%d%d",$n,$m);
if($n*2<=$m){
	$count = $n;
  	$m -= $n*2;	
}elseif($n==0 || $n==1 || $m==0){
  echo "0";
  exit;
}else{
  echo (int)($m/2);
  exit;
}

$count += (int)($m/4);
echo $count;