let letterToInt c = int_of_char c -65;;

let cellname_to_coord cn =
  let n = String.length (fst cn) and column = ref  0 in
                           for k=0 to (n-1)
                           do  (column := !column*26 + letterToInt (fst cn).[k])
                           done;
                           (snd cn -1, !column)
     ;;

let intToLetter c =String.make 1 (char_of_int (c + 65));;

let rec decTovingtsixmal  = function
  | n when n<26 -> [n]
  |n -> (n mod 26)::(decTovingtsixmal (n/26) );;

let coord_to_cellname co =
  let column_nbr = List.rev (decTovingtsixmal (snd co)) in
  (String.concat "" (List.map intToLetter column_nbr), fst co +1);;