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 Python (3.4.3) (judge verdict: Accepted)

N,M=map(int,input().split()) #SがN個、cがM個
Ans=0 #答えを入れる変数
if 2*N<=M: #cc→Sを使わないとcが余る場合
  Ans+=N
  M=M-2*N
  Ans+=M//4
  print(Ans)
elif 2*N>M: #cc→Sを使わないとSが余る場合
  Ans+=M//2
  print(Ans)