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: Time Limit Exceeded)

# -*- coding:utf-8 -*-
N, M = map(int, input().split())
if M > 0:
    if N*2 <= M:
        print((N+M//2)//2)
    else:
        ans = 0
        while True:
            N -= 1
            M -= 2
            if M >= 0 and N >= 0:
               ans += 1
            else:
                break
        print(ans)
else:
    print(0)