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>
using namespace std;
#define pi acos(-1)
#define IOS ios_base::sync_with_stdio(0); cin.tie(); cout.tie();
#define fi first
#define se second
#define pf push_front
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define debug(val) cerr << "Value " << #val << " : " << val << '\n';
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
const ll mod = 1e9 + 7;
const ll inf = 0x3f3f3f3f;
const ld epsilon = 10e-9;
const ll nax = 0;
ll s, c;
	
int main(void){
	IOS
	cin >> s >> c;
	ll ans;
	if(c>2*s){
		ans=(c+2*s)/4;
	}
	else{
		ans=min(c/2, s);
	}
	cout << ans << '\n';
}