need help in improving my boring-repeat function

[C K Kashyap]

Hi,
I've written a function to do some repeated insertions of lines like this -

(defun boring-repeat (count str)
  (interactive "sEnter count: \nsEnter format string: \n")
  (dotimes (i (string-to-number count))
    (insert (format str i))))

I was wondering how I could modify it so that I could optionally take a
function that could modify "i"

So if I call boring-repeat with 2 and hello%2d -> I'd get hello00 hello02
but say I could want hello01 and hello 02 or someother transformation on i

How can I go about implementing it?

Regards,
Kashyap