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 n = read_int ()
let s = read_line ()

let rec f maxim now str =
  let len = String.length str in
  if len = 0 then maxim
  else if str.[0] = 'I' then
    f (max maxim (now + 1)) (now + 1) (String.sub str 1 (len - 1))
  else f maxim (now - 1) (String.sub str 1 (len - 1))

let () = f 0 0 s |> Printf.printf "%d\n"