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>
using namespace std;

#define times(n, i)      uptil(0, n, i)
#define rtimes(n, i)     downto((n) - 1, 0, i)
#define upto(f, t, i)    for(int _##i = (t), i = (f); i <= _##i; i++)
#define uptil(f, t, i)   for(int _##i = (t), i = (f); i <  _##i; i++)
#define downto(f, t, i)  for(int _##i = (t), i = (f); i >= _##i; i--)
#define downtil(f, t, i) for(int _##i = (t), i = (f); i >  _##i; i--)

#define ln << endl

const int MOD = 1e9 + 7;

int main() {
    long long N, M; cin >> N >> M;

    if(N > M / 2)
        cout << M / 2;
    else
        cout << N + (M - N * 2) / 4 ln;

    return 0;
}