Extract First Elements of Arrays

Background

Dawei is processing some data and needs to extract key information from two arrays.

Problem Description

Given two integer arrays, $a$ and $b$, of any length, return a new array with the first element of each array. If either array is length $0$, ignore that array.

Input Format

The input consists of a single line. This line contains two strings representing integer arrays, where elements of each array are space-separated and enclosed in square brackets []. The two array strings are separated by a single space.

[element1 element2 ...] [element1 element2 ...]

Output Format

Output a new array containing the extracted elements. Elements are comma-separated and enclosed in square brackets [].

[element1, element2]

Sample

[1 2 3] [7 9 8]

[1, 7]

[1] [2]

[1, 2]

[1 7] []

[1]

Sample Explanation

For the first sample, the first element of array $a$ is $1$, and the first element of array $b$ is $7$. Merging them results in [1, 7].

Constraints

Time limit: $1$s, Memory limit: $1024$KiB for each test case.