What range have 1st step? For example, for MEDUIM (period == 500) is it [0..499] or [0..500] ?
The same question for last step: [Tmax-perion, Tmax-1] or [Tmax-period,Tmax] ?

And, output is defined incorrectly a bit: "In the first line output the number of “PERFECT” step-periods, ..." - any word about word "Perfect" in output.

no comments.

Follow the format, described in sample.

Range is of couse [0;500)

It's quite obvious. We have only three logical possibilities for that:
[0;500] is ambiguous because it overlaps with [500;1000].
(0;500), [0;500) and (0;500] can be tested vs. input.