let () =
  let rec charlist_of_string str n i =
    if i = n then []
    else str.[i] :: charlist_of_string str n (i+1) in
  let rec search lst target = match lst with
    | [] -> raise Not_found
    | h :: t -> if h = target then t else h :: search t target in
  Scanf.scanf "%s\n" @@ fun s ->
  let lst = ref (charlist_of_string s (String.length s) 0) in
  let flag = ref true in
  let ans = ref 0 in
  while !flag do
    try 
      let l = search !lst 't' in
      let l = search l 'r' in
      let l = search l 'e' in
      let l = search l 'e' in
      lst := l; ans := !ans + 1
    with Not_found -> flag := false
  done;
  Printf.printf "%d\n" !ans