The next several questions pertain to the following scenario: A study of 1000 people was conducted. 4 of them had chronic hepatitis C at baseline; an additional 6 developed hepatitis C over the course of the 1-year follow-up. This is what happened to the 10 cases (the remaining 990 people lived and were followed for the entire year, disease-free).

person 1: prevalent case at baseline; lived 12 months.
person 2: prevalent case at baseline; died after 6 months.
person 3: prevalent case at baseline; died after 10 months
person 4: prevalent case at baseline; died after 1 month
person 5: incident case diagnosed after 2 months; lived the rest of the year
person 6: incident case diagnosed after 3 months; died at the 6- month mark (so lived 3 months with hepC)
person 7: incidence case diagnosed after 3 months; lived the rest of the year
person 8: incident case diagnosed after 4 months; died 1 month later
person 9: incident case diagnosed after 6 months; lived the rest of the year
person 10: incident case diagnosed after 11 months; lived the rest of the year

Required:
What is the denominator, if we were to calculate prevalence in the middle of the 5th month?