Given an array of driver's ratings over N days.
Value over a period = (Contiuous sum * Minimum rating in that period)

eg: [3, 1, 6, 4, 5, 2]
Value could be (3+1+6+4+5+2) * 1 = 21.

Find the maximum value.
Here max value is (6+4+5) * 4 = 60.

O(N2) won't pass most test cases.