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 Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

(defun split (str delim)
  (let ((res (make-array 1 :element-type 'string
                           :fill-pointer 0
                           :adjustable t)))
    (loop for i from 0 below (length str)
          with start = 0
          when (eq (char str i) delim)
          do (vector-push-extend (subseq str start i) res)
             (setf start (1+ i))
          finally (let ((tail (subseq str start)))
                    (when tail
                      (vector-push-extend tail res))))
    res))

(let* ((line (map 'vector #'parse-integer (split (read-line) #\Space)))
       (n (aref line 0))
       (m (truncate (aref line 1) 2))
       (res 0)
       (nmin (min n m)))
  (incf res nmin)
  (decf n nmin)
  (decf m nmin)
  (incf res (truncate m 2))
  (format t "~A~%" res))