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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
#define fast ios::sync_with_stdio(false), cin.tie(0);
#define ll long long
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define endl '\n'

const int M = 1e9+7;

using namespace std;

main()
{
    fast;
    ll n,m;
    cin>>n>>m;
    if (n==m/2)
        cout<<n<<endl;
    else if (n<m/2)
    {
        m-=2*n;
        cout<<n+m/4<<endl;
    }
    else
        cout<<m/2<<endl;
}