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<iostream>
#include<cstdio>

#include<vector>
#include<string>

#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;
const ll INF = 1e12+1;
template <class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return 1;} return 0;}
template <class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return 1;} return 0;}

ll N, M;
//s N c M
//cを2K個K個のsに変換するとして

//s N+K c M-2K
//この時 min(N+K,(M-2K)/2)個ができる

//(N+K) * 2 = M-2K
//4K = M - 2N

//if (M <= 2N) M/2

int main() {
    cin >> N >> M;
    if (M <= 2 * N) {
        cout << M/2 << endl;
        return 0;
    }
    ll K = (M - 2 * N) / 4;

    cout << min(N+K,(M-2*K)/2) << endl;

}