Design a C# program to continuously receive a 4-digit year and calculate and tell whether it is a leap year.

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were.

In other words: Leap years occur mostly every 4 years, but every 100 years we skip a leap year unless the year is divisible by 400.