class Passenger:
   
    def __init__(self):
        self.tap_in_time = None
       
passengers = {}
time_increments = []


def tapIn( cardId, station, time ):
    if cardId in passengers:
        passengers[cardId].tap_in_time = (station, time)
    else:
        passengers[cardId] = Passenger()
        passengers[cardId].tap_in_time = (station, time)
   

def tapOut( cardId, station, time ):
    tap_station, tap_time = passengers[cardId].tap_in_time
    time_increment = time-tap_time
    time_increments.append((tap_station, station, time_increment))

def getAverage( startStation, endStation ):
   
    prev_average = 0
    prev_quantity = 0
   
    for (tap_in_station, tap_out_station, times) in time_increments:
       
        if tap_in_station == startStation and tap_out_station == endStation:
           
            new_quantity = prev_quantity+1
           
            new_average = ((prev_average * prev_quantity) + times)/new_quantitiy
           
            prev_average = new_average
            prev_quantity = new_quantitiy
   
    return prev_average
       
   
   
def __main__:
    tapIn( 4000, "A", t0)
    tapIn( 5000, "C", t1 )
    tapIn( 6000, "A", t2 )
    tapOut( 4000, "D", t3)
    tapOut( 5000, "E", t4 )
    tapIn( 7000, "R", t5 )
    tapOut( 6000, "X", t6 )
    tapOut( 7000, "X", t7 )
    ..
    ..
    ..
    ..
   
    getAverage( startStation, endStation )
   
	tapOut( 4000, "D", t13)
    tapOut( 5000, "E", t14 )
    tapIn( 7000, "R", t15 )
    tapOut( 6000, "X", t16 )
    tapOut( 7000, "X", t17 )
   
	getAverage( startStation, endStation )