parameter unit;
storage mutez;                    # How much you have to send me
code {CDR; DUP;                 # Get the amount required (once for comparison, once to save back in storage)
      AMOUNT; CMPLT;            # Check to make sure no one is wasting my time
      IF {FAIL}                 # Reject the person
         {NIL operation;PAIR}}  # Finish the transaction