card 21 trick

[SummoningZ]

Hi, I have a coding project for school which involves me making a program to do the 21 card trick in python.
I have started to make the program but am stuck on why it is not running, here is what I have at the moment.

first = ("JS","4C","KC","3H","5H","AD","10H")
second = ("9H","7S","JD","6D","JC","2D","QC")
third = ("5C","JH","4S","QS","8D","9D","4H")

def packet(first,second,third):
  for i in range(0,21,3):
    first.insert(0, packet[i])
    second.insert(0, packet[i+1])
    third.insert(0, packet[i+2])

print("1: " + " ".join([str(card) for card in first]))
print("2: " + " ".join([str(card) for card in second]))
print("3: " + " ".join([str(card) for card in third]))

selection = int(input("> "))
if selection == 1:
  packet.extend(second)
  packet.extend(first)
  packet.extend(third)
elif selection == 2:
  packet.extend(first)
  packet.extend(second)
  packet.extend(third)
elif selection == 3:
  packet.extend(first)
  packet.extend(third)  
  packet.extend(second)

print("You're thinking of the %s" % packet[10])

If someone can help me fix this so it does the card trick it will be greatly appreciated.
Thanks