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>
using namespace std;
#include<string>

int main(){
  int N,M;
  cin >> N >> M;
  string S_group;
  string C_group;
  for(int i=0;i<N;++i){
    S_group+='S';
  }
  for(int i=0;i<M;++i){
    C_group+='C';
  }
  int num_S=N;
  int num_C=M;
  while(2*num_S<num_C){
    num_S+=1;
    num_C-=2;
  }
  if(2*num_S>num_C){
    cout << num_C/2;
  }
  else{
    cout << num_S;
  }
}