Sets and Relations Part 1

Let A={1,2,3,....,100} and R be a relation on A such that R={(a,b):a=2b+1}. Let (a1,a2),(a2., a3),(a3,a4),...,(ak,ak+1) be a sequence of k elements of R such that the second entry of an ordered pair is equal to the first entry of the next ordered pair. Then the largest integer k, for which such a sequence exists, is equal to: