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 <bits/stdc++.h>
using namespace std;

int n,m;

inline int read(){
	int x=0,w=0; char ch=0;
	while (!isdigit(ch))
		w|=(ch=='-'),ch=getchar();
	while (isdigit(ch))
		x=(x<<3)+(x<<1)+(ch-'0'),ch=getchar();
	return w?-x:x;
}

inline void write(int x){
	if (x<0) putchar('-'),x=-x;
	if (x>9) write(x/10);
	putchar(x%10+'0');
}

int main(){
	n=read();m=read();
	if ((n<<1)>m) write(m>>1);
	else if ((n<<1)==m) write(n);
	else {
		m-=(n<<1);
		m>>=2;
		write(n+m);
	}
	return 0;
}