Simplify the following text for a Grade 3 native English-speaking person.
Original: 2000 ( MM ) was a leap year that started on a Saturday in the Christian or Common Era , according to the Gregorian calendar . It was the last year of the 2nd millennium and the 20th century but the 1st of the 2000s decade .
Simplified: The year 2000 was the first year of the 2000s decade .