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 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

/*#define d*/

int main()
{
        unsigned long long S=0;
        unsigned long long c=0;
        unsigned long long numOfScc=0;

        scanf("%llu %llu", &S, &c);

        while(1)
        {
#ifdef d
                printf("%llu %llu %llu\n", S, c, numOfScc);
#endif

                if(S*2>c)
                {
                        numOfScc=numOfScc+(c/2);
                        c=0;
                        break;
                }
                else if(S*2==c)
                {
                        numOfScc=numOfScc+S;
                        S=0;
                        break;
                }
                else
                {
                        numOfScc=numOfScc+S;
                        c=c-2*S;
                        S=c/2/2;
                        c=c/2;
                }
        }

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

        return 0;
}