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 OCaml (4.02.3) (judge verdict: Accepted)

let get_2_ints () = Scanf.scanf "%d %d " (fun u v -> u,v)

let () =
  let (s,c) = get_2_ints ()
  in
  (
    let c_left = c-s*2 in
    if c_left >= 0 then (
      s + c_left / 4
    )else(
      let s_true = c / 2
      in s_true
    )
  )
  |> string_of_int |> print_endline