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 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define endl        '\n'
#define db          double
#define ld          long double
#define ll          long long
#define ull         unsigned long long
#define sqr(x)      (x) * (x)
#define gcd(a, b)   __gcd(a, b)
#define lcm(a, b)   ((a/gcd(a,b)) * b)
#define pf(x) 		push_front(x)
#define pb(x)       push_back(x)
#define eb(x)		emplace_back(x)
#define all(x)      (x).begin(), (x).end()
#define rall(x) 	(x).rbegin(), (x).rend()
#define sz(x) 		(int)x.size()
#define debug(x) 	cerr << #x << " = " << (x) <<endl
#define unsyncIO    ios_base::sync_with_stdio(0); cin.tie(0)

const ld PI = acos((ld)-1);
const int MOD = 1e9+7;
const ll INF = 1e18; 

using namespace std;

int main()
{
    //freopen("/home/taalpatar_shepai/Documents/my_codes/out.txt", "w", stdout);
    unsyncIO;
    long long n, m;
    cin >> n >> m;
    long long s = n, c = m;
    n = n * 2;
    m = m - n;
    m = m / 4;
    long long cnt = m + s;
    if(c < 2) cnt = 0;
    if(s >= c) cnt = c / 2;
    cout << cnt << endl;
    return 0;
}