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: Time Limit Exceeded)

#include<iostream>
#include<algorithm>
#include<queue>
#include<cmath>
#include<map>
#include<vector>
#include<iomanip>
using namespace std;
typedef long long ll;
ll inf = 100000000;
ll v[205];
ll x[20000005];
ll a[10000005];
ll b[10000005];
ll dp[10005][10005];
ll ex = 1000000007;
int dx[4] = { 1,-1,0,0 };
int dy[4] = { 0,0,1,-1 };
typedef pair<ll, ll> P;
double q[200005];
ll gcd(ll a, ll b) {
	return b ? gcd(b, a % b) : a;
}

int main() {
	ll n, m;
	cin >> n >> m;
	if (n >= m) {
		cout << m / 2<< endl;
		return 0;
	}
	else {
		while (n * 2 < m) {
			m = m - 2;
			n = n + 1;
		}
		if (n * 2 == m) {
			cout << n << endl;
			return 0;
		}
		cout << n -1<< endl;
		return 0;
	}
}