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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.ByteString.Char8 as BS

main :: IO ()
main = do
  _ <- BS.getLine
  s <- BS.getLine :: IO BS.ByteString
  print $ calc s 0 0

calc :: BS.ByteString -> Int -> Int -> Int
calc xs n m
  | xs == mempty = m 
  | BS.head xs == 'I' = calc t ninc (max ninc m)
  | otherwise         = calc t ndec m
    where t = BS.tail xs
          ninc = n+1
          ndec = n-1