instruction: What is the least common birthday in the US other than Feb 29?
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.
response: The least common birthday in the United States between 1973 and 1999, excluding February 29, is December 25.