input: Write a python function to convert USD to GBP.
  assert convert_usd_to_gbp(130) == 100
  assert convert_usd_to_gbp(260) == 200
  assert convert_usd_to_gbp(0) == 0
output: def convert_usd_to_gbp(usd):
      exchange_rate = 0.7692  # Assume 1 USD = 0.7692 GBP
      return round(usd * exchange_rate)