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.

Input

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

Output

Print the answer.

Constraints

• 1 ≤ N,M ≤ 10^{12}

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

见题面 Input 部分

见题面 Output 部分