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: Runtime Error)

型のピースを 2 つ組み合わせて S 型のピースを 1 つ作ることができます。
n, m = gets.chomp.split(" ")
n = n.to_i # s
m = m.to_i # c

# Scc
num_c = n * 2 + m
#p num_c
ans =  num_c / 4
if ans * 2 > m
  puts m / 2
else
  puts num_c / 4 
end