S_n and a 1 minute delay.
   St(n): time person n arrives.
   Sts(n): time person n begins being served
   Stf(n): time person n is done being served and leaves
   Stf(n) = Sts(n) + 1
   Sts(n) = max(St(n), Stf(n -1))
   Recursively defined.  Can we reorient the process of recursion to
   define it as a sum with conditions?  Probably somehow?