Assume `"#"` is like a backspace in string. This means that string `"a#bc#d"` actually is `"bd"`
Your task is to process a string with `"#"` symbols.
## Examples
```
"abc#d##c"      ==>  "ac"
"abc##d######"  ==>  ""
"#######"       ==>  ""
""              ==>  ""
```
import re

def clean_string(s):
    return clean_string(re.sub('[^#]{1}#', '', s).lstrip('#')) if '#' in s else s

import re

def clean_string(s):
    return clean_string(re.sub('[^#]{1}#', '', s).lstrip('#')) if '#' in s else s
