Upvote:2
Whichever comes first - 50 days from (and including) the day you enter, or 29 Nov 2018. The number of days also includes the day you leave.
Upvote:2
Schengen visa have both a duration of stay and a validity period. The duration is the maximum number of days you can visit (the first and last day count full) and the validity is the period when you can take those days.
Usually the length of the validity period is longer than the duration of stay. That means you can shift your travel dates a bit, e.g. if a business meeting gets rescheduled, but you cannot extend your travel beyond the duration.