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)

include Math
define_method :max, -> (a,b) { a > b ? a : b }
define_method :min, -> (a,b) { a < b ?  a : b }
define_method :swap, -> (a,b) { a, b = b, a }
define_method :rep, -> (num, &block) { num.times do |i| block.call(i) end }
define_method :repl, -> (st,en, &block) { st.upto en-1 do |i| block.call(i) end }
define_method :array, -> (size,init = nil) { Array.new(size){init} }
define_method :darray, -> (size1, size2, init = nil) { Array.new(size1){Array.new(size2){init}} }
define_method :gi, -> () { gets.split.map(&:to_i) }
define_method :gs, -> () { gets.chomp }
define_method :putall, -> (obj) { obj.each do |o| puts o end }


n = gi
ans = n[0]
n[1] -= 2*n[0]
ans += n[1]/4 if n[1] > 0
puts ans