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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include<stdio.h>
int main(void)
{
    double a,b,sum=0;
    int c;
    scanf("%lf %lf",&a,&b);
    if(b<2||a<1)
        sum=0;
    else
    if(a>=b/2)
    {
        sum=b/2;
    }
    else if(a<b/2)
    {
        sum=a+(b-2*a)/4;
    }
    c=sum;
    if(sum-c>=0.5)
        sum=sum-1;
    printf("%.0f\n",sum);
    return 0;
}