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>
#define MEM(dp,i) memset(dp,i,sizeof(dp))
#define F first
#define S second
#define pb push_back
using namespace std;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
const int MX=1e5+9;
const ll inf=(1ll<<60);
const ll mod=1e9+7;
ll n,m,ans;
int main(){
    scanf("%lld%lld",&n,&m);
    ans=min(n,m/2);
    m-=n*2;
    ans+=max(m/4,0ll);
    printf("%lld\n",ans);
}