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;
using ll = long long;
using Graph = vector<vector<int>>;
#define ALL(x) (x).begin(), (x).end()
#define REP(i ,n) for(int i = 0; i < (int)(n); i++)
#define pb push_back
typedef vector<int>vint;
typedef vector<ll>vll;
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename A,typename B>inline bool chmin(A &a,const B &b){if(a>b){a=b;return true;}else{return false;}}
template<typename A,typename B>inline bool chmax(A &a,const B &b){if(a<b){a=b;return true;}else{return false;}}

int main()
{
    ll N,M;
    cin >> N >> M;
    ll cc = M/2;
    M %= 2;
    ll ans = 0;
    if(N <= cc){
        ans += N;
        cc -= N;
    }else{
        cout << cc << endl;
        return 0;
    }
    M += cc*2;
    ans += (M/4);
    cout << ans << endl;
}