Hexatridecimal notation is base 36 notation. The digits are '0' to '9' (with values 0 to 9) and 'A' to 'Z' (with values 10 to 35).
You are given a String numbers, where each element represents a positive integer in hexatridecimal notation. You must select exactly k digits (from the set of all digits - '0' to '9' and 'A' to 'Z') and replace all of their occurrences in all of the numbers with 'Z'. Then, calculate the sum of all the numbers.
Return the maximal possible sum you can get. The return value must be in hexatridecimal format with no leading zeroes.