let find_separator (sep : string) (k : int) (message : string) : int =
let l = String.length message in
let rec find_separator_aux i res =
if(res<l)
then(
let tmp = (String.get message res) in
if(i=k && tmp=sep.[0]) then (res)
else if (tmp='(') then (find_separator_aux (i+1) (res+1))
else if(tmp=')') then (find_separator_aux (i-1) (res+1))
else(find_separator_aux i (res+1));
)
else (-1);
in
(find_separator_aux 0 0)