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: Accepted)

import Control.Applicative ((<$>), (<*>), (<*), (*>), (<$))
import Control.Monad
import Data.List

main :: IO ()
main = do
  solve <$> getl (map read .words) >>= print

solve :: [Integer] -> Integer
solve [n, m]
  | 2 * n <= m = n + (m - 2 * n) `div` 4
  | otherwise = m `div` 2

getl :: (String -> a) -> IO a
getl f = f <$> getLine