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: Time Limit Exceeded)

input = gets.split().map(&:to_i)
puzzle_s = input[0]
puzzle_c = input[1]
puzzle_scc = 0

puzzle_s.times do
    if puzzle_c >= 2
        puzzle_scc += 1
        puzzle_c -= 2
    else
        break
    end
end

while (puzzle_c >= 4)
    puzzle_c -= 4
    puzzle_scc += 1
end

puts "#{puzzle_scc}"