let string_of_char c = String.make 1 c ;;

let string_apply f s =
  let rec string_apply2 f s = function
    n when n = String.length s -> ""
    | n -> string_of_char ( f s.[n]) ^ string_apply2 f s (n+1)
  in string_apply2 f s 0 ;;
let caesar s n = string_apply (function c ->
  if c < 'a' then c
  else if c > 'z' then c
  else Char.chr(((Char.code c - Char.code 'a' +n)mod 26 )+Char.code 'a')) s ;;

let length = Array.length Sys.argv ;;

let rec caesar_argv = function
    n when n = length -> caesar Sys.argv.(n-1) (int_of_string( Sys.argv.(n)))
  | n when n mod length = 2 -> caesar Sys.argv.(n-1) (int_of_string( Sys.argv.(n))) ^"\n"^  caesar_argv (n+1)
  | n -> caesar_argv (n+1)
in caesar_argv 3 ;;

let _ = caesar_argv 3 ;;