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: Time Limit Exceeded)

#include<stdio.h>
int main(void)
{
	long N, M,i=0;
	long pair=0;
	scanf("%ld %ld",&N, &M);

	if (N < M * 2) {
		while (1) {
			if ((N - i) * 2 <= M) {
				pair = N - i;
				M = M - (N - i) * 2;
				break;
			}
			else {
				if (M <= 0)break;
				i++;
			}
		}
	}
	else {
		while (N) {
			M = M / 2;
			if (M) {
				pair++;
				N--;
			}
			else
				break;
		}
	}
	pair += M / 4;

	printf("%ld\n",pair);
	return 0;
}