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 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include<stdio.h>
#include<math.h>


int main(){
  long long n,m;
  scanf("%lld",&n);
  scanf("%lld",&m);

  if(n*2>=m){
    if(m%2==0){
      printf("%lld\n",m/2);
    }
    else{
      printf("%lld\n",(m-1)/2);
    }
  }

  else{
    
    while(n*2<m){
      n++;
      m=m-2;
    }
    if(m%2==0){
      printf("%lld\n",m/2);
    }
    else{
      printf("%lld\n",(m-1)/2);
    }
    
    
  }
  return 0;

}