Suppose there is a pair of newborn bunnies in the pasture in the first month, each pair of male and female bunnies grew into a large male and female rabbits after two months later. After three months from the start, each pair of male and female rabbit can give birth to a pair of small bunnies every month. If the rabbits can live forever, how many pair of rabbits in the pasture in the first N month?
"1<=N<=90 is very important"
I think the hint is enough and clear.