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: Wrong Answer)

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

#define print printf("%ld", answer)
int main(void){
  long N, M, answer, k, l;
  

  scanf("%ld", &N);
  scanf("%ld", &M);

  if(N>=0&&M<=1000000000001)
    {
      
  if(M%2==0)
    {
      k = M/2;
  if(N>=k)
    {
      answer = k;
    }
  if(N==k-1)
    {
      answer = N;
    }
  if(N<=k-2)
    {
      if(k%2==0)
	{
	  l = k/2;
	  answer = N + l;
      	}
      if(k%2==1)
	{
	  l = (k-1)/2;
	  answer = N + l;
	  
	}
    }
    }


  
  if(M%2==1)
    {
      k = (M+1)/2;

      if(N>=k-1)
	{
	  answer=k-1;
	}
      if(N==k-2)
	{
	  answer = N;
	}
      else
	{
	  if((k-1-N)%2==0)
	    {
	      l = (k-1-N)/2;
	      answer = N + l;
	    }
	  else
	    {
	      l = (k-2-N)/2;
	      answer = N + l;
	    }
	}
    }
    }
  print;
  
  return 0;
}