For string "A": A
For string "ABC": Hello
For string "AB": Hello
For string "AC": A
For string "ACB": A
For string "D": failure
For string "ABCD": Hello
For string "": 

Output: ``` For string "A": A For string "ABC": Hello For string "AB": Hello For string "AC": A For string "ACB": A For string "D": failure For string "ABCD": Hello For string "": ```