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 <bits/stdc++.h>
using namespace std;
#define rep0(i,n) for(ll (i) = 0; (i) < (n); ++(i))
#define rrep0(i,n) for(ll (i) = (n) - 1; (i) >= 0; --(i))
#define rep1(i,n) for(ll (i) = 1; (i) < (n); ++(i))
#define rrep1(i,n) for(ll (i) = (n) - 1; (i) >= 1; --(i))
#define nfor(i,a,b) for(ll (i) = (a); (i) < (b); ++(i))
#define ll long long
#define mod (1000000007)
#define YES cout << "YES" << endl;
#define Yes cout << "Yes" << endl;
#define yes cout << "yes" << endl;
#define NO cout << "NO" << endl;
#define No cout << "No" << endl;
#define no cout << "no" << endl;
#define all(x) (x).begin(),(x).end()

ll gcd(ll a,ll b){
    if(b == 0) return a;
    return gcd(b,a%b);
}

ll lcm(ll a,ll b){
    ll g = gcd(a,b);
    return a / g * b;
}

ll fac(ll n){
    ll t = 1;
    rep1(i, n + 1)t *= i;
    return t;
}

int main()
{
    ll n,m;
    cin >> n >> m;
    if (m/2 <= n) {
        cout << m / 2 << endl;
    }else{
        cout << n + (m - n * 2) / 4 << endl;
    }
    return 0;
}