Problem Statement  
You are walking down the escalator to catch a subway train.
The escalator itself moves at a speed of Ve meters per minute.
You can walk down the escalator at a relative speed of Vy meters per minute.
The length of the escalator is L meters.
Trains arrive T minutes apart.
Let t be the time between your arrival to the station if you stand still on the escalator and the arrival of the last train before your arrival. Assume that t is a random variable uniformly distributed between 0 and T. Return the probability of catching an earlier train if you choose to walk down the escalator instead of standing still on it.  
Definition  
 
Notes  
  The returned value must have an absolute or relative error less than 1e9.  
Constraints  
  Ve will be between 10 and 60, inclusive.  
  Vy will be between 1 and 10, inclusive.  
  L will be between 10 and 100, inclusive.  
  T will be between 2 and 20, inclusive.  
Examples  
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