You are looking for a place to park your car on a suburban street. You can park at any position that meets the following requirements:
1. It is not directly in front of a private driveway.
2. It is not directly in front of a bus stop.
3. It is not 5 meters before a bus stop.
4. It is not 10 meters before a bus stop.
5. It is not directly in front of a side-street.
6. It is not 5 meters before a side-street.
7. It is not 5 meters after a side-street.
The street will be represented as a String, where each character describes a section of the street 5 meters in length. So the first character describes the first 5 meters of the street, the second character describes the next 5 meters and so on. street will use 'D' for driveway, 'B' for bus stop, 'S' for side-street and '-' for all other sections of the street. A position is directly in front of an object if it has the same index as the object in street. A position is before an object if its index is lower than the index of the object in street. Finally, a position is after an object if its index is higher than the index of the object in street.
Given the street return the total number of possible parking spaces on that street.