let cosX a b c = a ** 2. +. b ** 2. -. c ** 2.
let sinX c = sqrt (1. -. c ** 2.)
let () =
  Scanf.scanf "%d %d %d\n"
    (fun a b c ->
       let af = float_of_int a in
       let bf = float_of_int b in
       let cf = float_of_int c in
       0.5 *. af *. bf *. sinX (cosX af bf cf))
  |> int_of_float |> print_int