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 Ruby (2.3.3) (judge verdict: Wrong Answer)

# ピース数取得
peaces = STDIN.gets.strip.split(' ')
peace_s = peaces[0].to_i
peace_c = peaces[1].to_i

# 作成個数
count = 0

if peace_s < peace_c * 0.5
  count = peace_s
  peace_c -= peace_s * 2
  count += ( peace_c / 3 ).floor
else
 count = ( peace_c * 0.5 ).floor
end

puts count