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 JavaScript (node.js v5.12) (judge verdict: Accepted)

function Main (input) {
	var inputArr = input.split(' ');
	var sNum = Number(inputArr[0]);
	var cNum = Number(inputArr[1]);
	var result = 0;
	// Sを使う組み合わせ
	if (sNum > (cNum/2)) {
		result += Math.floor(cNum/2);
	} else {
		result += sNum;
		cNum -= result * 2;
		result += Math.floor(cNum/4)
	}
	console.log(result);
}
// Main("12345 678901");
Main(require("fs").readFileSync("/dev/stdin", "utf8"));