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 math.max
object Main extends App {
    val n = io.StdIn.readInt
    val s = io.StdIn.readLine

    def rec(str: String, count: Int, max_count: Int): Int = {
        if (str.isEmpty) max_count
        else str.head match {
            case 'I' => rec(str.tail, count+1, max(count+1, max_count))
            case 'D' => rec(str.tail, count-1, max(count-1, max_count))
        }
    }

    val result = rec(s, 0, 0)
    println(result)
}