What's the magic word ?

What's the magic word - For this task we had to ask the user "What's the magic word?". This was based on the children that don't say the magic word, in this case please.We also needed to program it so that it would accept upper,lower and mixed letters.
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s = ""
while s != 'please' not in s.lower():
  s = input("What's the magic word?")
print("OK!")