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: Wrong Answer)

#include <stdio.h>
typedef long long unsigned int u64;


u64 solve(u64 n, u64 m) {
    if(n > 2 * m) return m / 2;
    if(n == 2 * m) return n;
    if(n < 2 * m) return (n + m / 2) / 2;
}

int main(void) {
    u64 n, m;
    scanf("%llu%llu", &n, &m);
    printf("%llu", solve(n, m));
    return 0;
}