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)

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <cmath>
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define MA(i,j) make_pair(i,j)
#define PA pair<int,int>
#define PB push_back
#define PQ priority_queue<int>
#define PGQ priority_queue<int,vector<int>,greater<int> >
#define VE vector<int>
#define VP vector<PA>
#define YES(i) cout<<(i?"YES":"NO")<<endl
#define Yes(i) cout<<(i?"Yes":"No")<<endl
#define MOD 1000000007
#define INF 1000000007
using namespace std;
//
int main(){
  long long N,M,cnt=0;
  cin>>N>>M;
  if(2*M<=N){
    cnt+=M;
  }else{
    cnt+=N;
    M-=2*N;
    cnt+=M/4;
  }
  cout<<cnt<<endl;
  return 0;
}