Definition: In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.
Input: Dr. Spencer Reid:  The number sequence starts at 3553 and ends ... at _ 87 _ . Clark was killed on January 14th , 87 days before scheduled release date of April the 11th Working backwards and taking into account the 2008 , 2012 leap years april 9th 2004 exactly when Clark began prison term .

sequence