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 Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

main = do
  [s,c] <- map read . words <$> getLine :: IO [Int]
  print $ solve s c 

solve :: Int -> Int -> Int
solve s c
  | s >= 2*c = s + (c-s) `div` 4
  | otherwise = 
    let 
      ccs = c `div` 2
    in
      if s >= ccs then s else s + (c-s*2) `div` 4