A decimal number can be converted to its Hexspeak representation by
first converting it to an uppercase hexadecimal string, then replacing all occurrences
of the digit 0 with the letter O, and the digit 1
with the letter I. Such a representation is valid if
and only if it consists only of the letters in the set {"A", "B", "C", "D", "E",
"F", "I", "O"}.
Given a string num representing a decimal integer N,
return the Hexspeak representation of N if it is valid, otherwise
return "ERROR".
Example 1:
Input: num = "257" Output: "IOI" Explanation: 257 is 101 in hexadecimal.
Example 2:
Input: num = "3" Output: "ERROR"
Constraints:
1 <= N <= 10^12