Problem:
Score : 200 points

Problem Statement

You have an integer variable x.
Initially, x=0.

Some person gave you a string S of length N, and using the string you performed the following operation N times.
In the i-th operation, you incremented the value of x by 1 if S_i=I, and decremented the value of x by 1 if S_i=D.

Find the maximum value taken by x during the operations (including before the first operation, and after the last operation).

Constraints

1≤N≤100

|S|=N

No characters except I and D occur in S.

Input

The input is given from Standard Input in the following format:

N
S

Output

Print the maximum value taken by x during the operations.

Sample Input 1

5
IIDID

Sample Output 1

2

After each operation, the value of x becomes 1, 2, 1, 2 and 1, respectively. Thus, the output should be 2, the maximum value.

Sample Input 2

7
DDIDDII

Sample Output 2

0

The initial value x=0 is the maximum value taken by x, thus the output should be 0.

Solution in OCaml (4.02.3) (judge verdict: Accepted)

let id a = a
let n = Scanf.scanf "%d\n" id
let repeat f =
  let rec loop acc = function
    | 0 -> List.rev acc
    | n -> loop (f () :: acc) (n-1) in
  loop []

let r = repeat (fun () -> Scanf.scanf "%c" id) n

let rec ans x list = function
  | [] -> list
  | a :: rest ->
     match a with
     | 'I' -> ans (x+1) ((x+1) :: list) rest
     | 'D' -> ans (x-1) ((x-1) :: list) rest
     | _   -> ans x (x :: list) rest

let anslist = ans 0 [] r 

let rec maxlist l x =
  match l with
  | [] -> x
  | a :: rest -> if a > x then maxlist rest a else maxlist rest x
 
let saidai = maxlist anslist 0
	
let () = Printf.printf "%d\n" saidai