open System

let Puts = Console.WriteLine : 'a -> unit
let Reads () = Console.ReadLine().Split()
let ReadDouble () = Reads() |> (fun x -> x.[0], x.[1])
let ReadTriple () = Reads() |> (fun x -> x.[0], x.[1], x.[2])
let ReadQuadruple () = Reads() |> (fun x -> x.[0], x.[1], x.[2], x.[3])

let FuncDouble f1 f2 (t1, t2) = (f1 t1, f2 t2)
let FuncTriple f1 f2 f3 (t1, t2, t3) = (f1 t1, f2 t2, f3 t3)
let FuncQuadruple f1 f2 f3 f4 (t1, t2, t3, t4) = (f1 t1, f2 t2, f3 t3, f4 t4)


// main code

Console.ReadLine() |> ignore
let s = Console.ReadLine()

let f (maxv, current) c =
    let next =
        match c with
        | 'I' -> current + 1
        | _ -> current - 1
    in (max maxv next, next)

List.fold f (0, 0) (Seq.toList s) |> fst |> Puts
