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 <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <map>
#include <unordered_map>
#include <set>
#include <queue>
using namespace std;
#define ALL(x) (x).begin(),(x).end()
#define SZ(x) int((x).size())
#define OUT(x) cout << (x) << endl
typedef long long ll;
typedef vector<int> V;
typedef vector< vector<int> > VV;
typedef pair<int, int> P;
typedef map<string, int> M;
typedef unordered_map<int, int> HM;
typedef set<int> S;
typedef multiset<int> MS;
typedef queue<int> Q;

int main(){
    ll n,m; cin>>n>>m;
    ll ans = min(n,m/2);
    n -= ans;
    m -= ans*2;
    if(m > 1)
        ans += m/4;
    OUT(ans);
}