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 JavaScript (node.js v5.12) (judge verdict: Accepted)

'use strict';

const input = require('fs').readFileSync('/dev/stdin', 'utf8').trim().split('\n');
const NM = input[0].trim().split(' ');
const N = parseInt(NM[0]);
const M = parseInt(NM[1]);

console.log(
    (M <= 2 * N) ?
    Math.floor(M / 2) :
    Math.floor((2 * N + M) / 4)
);