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: Wrong Answer)

using System;

namespace C_SccPuzzle {
    class Program {
        static void Main(string[] args) {
            var str = Console.ReadLine().Split(' ');
            var N = long.Parse(str[0]);
            var M = long.Parse(str[1]);
            var ans = 0L;
            var margin = 2;
            var x = (M - 2 * N) / 2;
            for (long y = x - margin; y <=x + margin; y++) {
                ans = Math.Max(ans, Math.Min(N + y / 2, (M - y) / 2));
            }
            Console.WriteLine(ans);
        }
    }
}