input: Write a python function to subtract timestamps.
  assert subtract_timestamps("4:00:00 AM", "3:00:00 PM") == "12:00"
  assert subtract_timestamps("10:30:00 AM", "8:20:00 AM") == "2:10"
  assert subtract_timestamps("6:00:00 PM", "4:00:00 PM") == "2:00"
output: def subtract_timestamps(start, end):
      from datetime import datetime
  
      fmt = "%I:%M:%S %p"
      start_dt = datetime.strptime(start, fmt)
      end_dt = datetime.strptime(end, fmt)
  
      diff = end_dt - start_dt
      if diff.days < 0:
          diff = datetime.strptime("1:00:00 AM", fmt) - start_dt + end_dt
  
      hours, remainder = divmod(diff.seconds, 3600)
      minutes, _ = divmod(remainder, 60)
      
      return f"{hours}:{minutes:02d}"