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 PyPy3 (2.4.0) (judge verdict: Accepted)

n,m=map(int,input().split())
if 2*n>=m:
    print(m//2)
else:
    k1 = (m-n*2)//4
    k2 = k1+1
    k3 = max(k1-1,0)
    r1 = min(n+k1,(m-k1*2)//2)
    r2 = min(n+k2,(m-k2*2)//2)
    r3 = min(n+k3,(m-k3*2)//2)
    print(max(r1,r2,r3))