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: Accepted)

#include <bits/stdc++.h>
#define ls (o << 1)
#define rs (o << 1 | 1)
#define mid ((L + R + 1) >> 1)
using namespace std;
const int MAXN = 200050;
const int mod = 998244353;
typedef long long LL;
int main() {
#ifdef TEST
	freopen("input.txt", "r", stdin);
#endif
	LL a, b;
	cin >> a >> b;
	LL L = 0, R = a + b;
	while (L < R) {
		if (b >= mid + mid && a + (b - mid - mid) / 2 >= mid) {
			L = mid;
		} else {
			R = mid - 1;
		}
	}
	cout << L << endl;
	return 0;
}