A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lowercase English letters (no punctuation).

- For example, `"Hello World"`, `"HELLO"`, and `"hello world hello world"` are all sentences.

You are given a sentence `s`​​​​​​ and an integer `k`​​​​​​. You want to truncate `s`​​​​​​ such that it contains only the first `k`​​​​​​ words. Return `s`​​​​​​ after truncating it.

Example 1:

    Input: s = "Hello how are you Contestant", k = 4
    Output: "Hello how are you"
    Explanation:
    The words in s are ["Hello", "how" "are", "you", "Contestant"].
    The first 4 words are ["Hello", "how", "are", "you"].
    Hence, you should return "Hello how are you".

Example 2:

    Input: s = "What is the solution to this problem", k = 4
    Output: "What is the solution"
    Explanation:
    The words in s are ["What", "is" "the", "solution", "to", "this", "problem"].
    The first 4 words are ["What", "is", "the", "solution"].
    Hence, you should return "What is the solution".

Example 3:

    Input: s = "chopper is not a tanuki", k = 5
    Output: "chopper is not a tanuki"

Constraints:

- `1 <= s.length <= 500`
- `k` is in the range `[1, the number of words in s]`.
- `s` consist of only lowercase and uppercase English letters and spaces.
- The words in `s` are separated by a single space.
- There are no leading or trailing spaces.