let path _ =
  let siz = size graf in
  let values = Array.make siz (-1) in
  let rec dfs w =
    if values.(w) >= 0 then values.(w) else
    let sasiedzi = neighbours graf w in
    let f acc sasiad =
      if sasiad < w then max (dfs sasiad) acc
      else acc
    in
    let fold_result = List.fold_left f 0 sasiedzi + 1 in
    values.(w) <- fold_result;
    fold_result
  in
  let answer = ref 0 in
  for i = siz - 1 downto 0 do
    answer := max !answer (dfs i - 1);
  done;
  !answer