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: Time Limit Exceeded)

#include<iostream>
#include<string>
#include<string.h>
#include<map>
#include<set>
#include<vector>
#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<queue> 
using namespace std;
int main() 
{long long n,m;
 cin>>n>>m;
 if (2*n>m){cout<<m/2; system("pause"); return 0;}
 while (2*n<m){
 n+=1;
 m-=2;
 if (2*n>m){
 cout<<n-1;
 system("pause");
 return 0;}}
 cout<<n;
 system("pause");
 return 0;
}