Sequences word problems

Zhang Lei tracked the size of the bear population in a nature reserve. The first year, there were $1000$1000 bears. Sadly, the population lost $10\%$10, percent of its size each year.

Let $f(n)$f, left parenthesis, n, right parenthesis be the number of bears in the reserve in the $n^\text{th}$n, start superscript, start text, t, h, end text, end superscript year since Zhang Lei started tracking it.

$f(1)=$f, left parenthesis, 1, right parenthesis, equals