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)

#define _GLIBCXX_DEBUG
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
#include<iostream>
#include<vector>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
#include<string>
#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)n; i++)
#define rep2(i,s,n) for(int i=s;i< (int)n; i++)
#define ll long long 
#define all(v) v.begin(),v.end()
using namespace std;
int main(){
  ll n ,m ; cin >>n>>m;
  if(2*n>m){
    cout<<m/2<<endl;
    return 0;
  }
  ll l=m/4-n/2;
  ll a=max({min(n+l,(m-2*l)/2),min(n+l+1,(m-2*l-2)/2),min(n+l-1,(m-2*l+2)/2)});
  cout <<a<<endl;
}