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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using static System.Console;

class Program {
	static void Main() {
		var N = NextLong();
		var S = ReadLine();
		var cnt = 0;
		var ans = 0;

		foreach (var c in S) {
			switch (c) {
				case 'I':
					cnt++;
					break;
				case 'D':
					cnt--;
					break;
				default:
					break;
			}
			ans = Math.Max(ans, cnt);
		}
		WriteLine(ans);
	}
	static long NextLong() {
		return long.Parse(NextString());
	}

	static string NextString() {
		var result = new List<char>();
		while (true) {
			int next = Read();
			if (next < 0)
				break;
			var nextChar = (char)next;
			if (!char.IsWhiteSpace(nextChar))
				result.Add(nextChar);
			else if (nextChar != '\r')
				break;
		}
		return string.Join("", result);
	}
}