I want to use a function to determine how many bonus tickets I should give
out at the end of each month. One (1) ticket for every three (3) apples sold.
For example, here is a table:

DATE #APPLES SOLD BONUS TICKETS
JAN 1 0
FEB 3 1

MAR 6 2
APR 8 2
MAY 9 3
JUN 12 4
JUL 15 5


PLEASE HELP!