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;
typedef long long unsigned int ll;

// definition {{{ 1

// scaning {{{ 2
#define Scd(x) scanf("%d", &x)
#define Scd2(x,y) scanf("%d%d", &x, &y)
#define Scd3(x,y,z) scanf("%d%d%d", &x, &y, &z)

#define Scll(x) scanf("%llu", &x)
#define Scll2(x,y) scanf("%llu%llu", &x, &y)
#define Scll3(x,y,z) scanf("%llu%llu%llu", &x, &y, &z)

#define Scc(c) scanf("%c", &c);
#define Scs(s) scanf("%s", s);
#define Scstr(s) scanf("%s", &s);
// }}} 2

// constants {{{ 2
#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
// }}} 2

// systems {{{ 2
#define Rep(x,y) for(int x = 0; x < y; x++)
#define Repe(x,y,z) for(int x = z; x < y; x++)
// }}} 2

// output {{{ 2
#define YesNo(a) (a)?printf("Yes\n"):printf("No\n");
// }}} 2

// }}} 1

int main() {

    ll n,m;

    Scll2(n,m);

    ll ans = 0;

    if( m/2 <= n ){
        ans = m/2;
    }else{
        ans += n;
        m -= n * 2;
        ans += m / 4;
    }

    printf ("%llu\n", ans);

    return 0;
}