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 Scala (2.11.7) (judge verdict: Accepted)

import scala.io.StdIn.readLine
import scala.unchecked

object Main extends App {
  val n = readLine.toInt
  val s = readLine.toArray

  println(0 max solve(0, s))

  def solve(x: Int, s: Array[Char]): Int = {
    if (s.isEmpty) x
    else {
      val newx = x + ((s.head: @unchecked) match {
        case 'I' =>  1
        case 'D' => -1
      })
      newx max solve(newx, s.tail)
    }
  }
}