let m = 1000000007
let ( +^ ) x y = (x + y) mod m
let ( -^ ) x y = x +^ (m - y)
let ( *^ ) x y = (x * y) mod m

let rec power ( * ) e m n =
  if n <= 0 then e
  else power ( * ) (if n land 1 = 0 then e else m * e) (m * m) (n lsr 1)

let perm n k =
  Array.fold_left ( *^ ) 1 @@
  Array.init k @@ fun i -> (i + n - k + 1) mod m
let comb n k = power ( *^ ) (perm n k) (perm k k) (m - 2)

let () = Scanf.scanf "%d %d %d" @@ fun n a b ->
  Printf.printf "%d\n" @@ power ( *^ ) 1 2 n -^ comb n a -^ comb n b -^ 1