Given a string `s` containing an out-of-order English representation of digits `0-9`, return the digits in ascending order.

Example 1:

    Input: s = "owoztneoer"
    Output: "012"

Example 2:

    Input: s = "fviefuro"
    Output: "45"

Constraints:

- `1 <= s.length <= 105`
- `s[i]` is one of the characters `["e","g","f","i","h","o","n","s","r","u","t","w","v","x","z"]`.
- `s` is guaranteed to be valid.