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: Wrong Answer)

// g++ macro.cpp -std=c++14
#include <bits/stdc++.h> //STL include
typedef long long ll;// long long int
const ll INF = 10000000000;//INFinity
using namespace std;//namespace

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}//transform
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//#define int long long // yabai

#define dump(x)  cout << #x << " = " << (x) << endl;// debug cout

#define FOR(i,a,b) for(int i=(a);i<(b);++i)// for macro
#define REP(i,n) for(int i=0;i<(n);++i)
#define REPR(i,n) for(int i=n;i>=0;i--)

#define ALL(obj) (obj).begin(),(obj).end()// iterator

#define pb(a) push_back(a)//push_back
#define mp make_pair// make_pair


int main(){

    ll n,m;
    ll ans=0;
    cin>>n>>m;

    if(n<m*2){
        ans+=n;
        m-=n*2;
        ans+=m/4;
    }else{
        ans+=n/2;
    }
    cout<<ans<<endl;
    
    return 0;
}