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

#include<iostream>
using namespace std;
long long int n,m,nd;
int main(){
    cin>>n>>m;
    nd=2*n;
    if(nd>m)cout<<m/2<<endl;
    else if(nd==m)cout<<n<<endl;
    else{
        m-=nd;
        m/=4;
        cout<<n+m<<endl;
    }
    return 0;
}