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)

main :: IO()
main = do
  _ <- getLine 
  str <- getLine
  putStrLn $ solve str

solve :: String -> String
solve str = show.snd $ foldl f (0,0) str
  where
    f :: (Int, Int) -> Char -> (Int, Int)
    f (x,m) 'I' = (x+1, max m (x+1))
    f (x,m) 'D' = (x-1,  m)
    f (x,m) _ = (x,m)