Complex sentence: A perimeter rule prohibits nonstop flights to or from points beyond 1,500 statute miles (2,400 km), but exceptions to the perimeter rule are flights on Saturdays and flights to Denver.
Split into simpler sentences: A perimeter rule prohibits nonstop flights to or from points beyond 1,500 statute miles (2,400 km). Exceptions to the perimeter rule are flights on Saturdays and flights to Denver.