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 C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

 class Program
    {
        static void Main(string[] args)
        {
            string line = System.Console.ReadLine().Trim();

            string[] Data = line.Split(' ');
            int N = int.Parse(Data[0]);
            int M = int.Parse(Data[1]);

            int count = 0;

            while (true)
            {
                N = N - 1;
                M = M - 2;

                if (M < 0)
                {
                    System.Console.WriteLine(count);
                    return;
                }

                if (N < 0)
                {
                    if (M >= 2)
                    {
                        N++;
                        M -= 2;
                    }
                    else
                    {
                        System.Console.WriteLine(count);
                        return;
                    }
                }

                count++;
            }           
        }
    }