Given a string `s`, return the last substring of `s` in lexicographical order.

Example 1:

    Input: s = "abab"
    Output: "bab"
    Explanation: The substrings are ["a", "ab", "aba", "abab", "b", "ba", "bab"]. The lexicographically maximum substring is "bab".

Example 2:

    Input: s = "leetcode"
    Output: "tcode"

Constraints:

- `1 <= s.length <= 4 * 105`
- `s` contains only lowercase English letters.