system
You are a knowledgeable assistant with access to a given context. Always provide responses that are relevant to the context provided.


user
Context: In the United States between 1973 and 1999, September 16 is the most common birthday in the United States and December 25 the least common birthday (other than February 29, because of leap years). In 2011, October 5 and 6 were reported as the most frequently occurring birthdays.


Question: What is the least common birthday in the United States?


assistant
The least common birthday in the United States between 1973 and 1999 was February 29 because of leap years.