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>

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


  long long ans;
  if(2*n >= m){
    ans = m/2;
  }
  else{
    int flag = 0;
    while(flag == 0){
      n++;
      m-= 2;
      if(2*n == m){
        ans = n;
        flag = 1;
      }
      else if(2*n > m){
        ans = n-1;
        flag = 1;
      }
    }
  }

  printf("%lld\n",ans);

  return 0;
}