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 Perl (v5.18.2) (judge verdict: Accepted)

use POSIX 'floor';
my $input = <STDIN>;
my @inputs = split(/ /,$input);
my $sPeace = int($inputs[0]);
my $cPeace = int($inputs[1]);
if($sPeace * 2 <= $cPeace){
	print floor($sPeace + ($cPeace - $sPeace * 2) / 4) + "\n";
} else {
	my $output = floor($cPeace / 2);
	if($output > $sPeace){
		$output = $sPeace;
	}
	print $output + "\n";	
}