fun tally (nt, nr, ne) =
    if TextIO.endOfStream TextIO.stdIn then (nt, nr, ne)
    else case TextIO.input1 TextIO.stdIn of
             SOME c => if c = #"t" then tally (nt + 1, nr, ne)
                       else if c = #"r" then tally (nt, nr + 1, ne)
                       else if c = #"e" then tally (nt, nr, ne + 1)
                       else tally (nt, nr, ne)
           | NONE => (nt, nr, ne)
        


val () =
    let
        val (numOfT, numOfR, numOfE) = tally (0, 0, 0)
        val ans = Int.min (numOfT, Int.min (numOfR, numOfE div 2))
    in
        print (Int.toString ans ^ "\n")
    end