Given a string s representing a list of numbers, find the five consecutive numbers that multiply to form the largest number. Specifically, given s return the index i to the first of those five numbers. You can assume the maximum product is unique.
Input s = '123454321' Output i = 3
since the product of [3 4 5 4 3] is larger than any of the alternatives.
Inspired by Problem 8 from Project Euler