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;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.Linq;
using System.IO;

class Program
{ 
    static void Main(string[]args)
    {
        Magatro m = new Magatro();
        m.Scan();
        m.Solve();
    }
}

public class Scanner
{
    private StreamReader Sr;
    private string[] S;
    private int Index;

    private const char Separator=' ';

    public Scanner()
    {
        Index = 0;
        S = new string[0];
        Sr = new StreamReader(Console.OpenStandardInput());
    }

    private string[] Line()
    {
        return Sr.ReadLine().Split(Separator);
    }

    public string Next()
    {
        string result;
        if (Index >= S.Length)
        {
            S = Line();
            Index = 0;
        }
        result = S[Index];
        Index++;
        return result;
    }
    public int NextInt()
    {
        return int.Parse(Next());
    }
    public double NextDouble()
    {
        return double.Parse(Next());
    }
    public long NextLong()
    {
        return long.Parse(Next());
    }
    public string[] StringArray(int index = 0)
    {
        Next();
        Index = S.Length;
        return S.Skip(index).ToArray();
    }
    public int[] IntArray(int index = 0)
    {
        return StringArray(index).Select(int.Parse).ToArray();
    }
    public long[]LongArray(int index = 0)
    {
        return StringArray(index).Select(long.Parse).ToArray();
    }

    public bool ScanToEnd(ref string s)
    {
        if (Sr.EndOfStream)
        {
            return false;
        }
        else
        {
            s = Sr.ReadLine();
            return true;
        }
    }
}

public class Magatro
{
    private int N;
    private string S;

    public void Scan()
    {
        Scanner sc = new Scanner();
        N = sc.NextInt();
        S = sc.Next();
    }

    public void Solve()
    {
        int x = 0;
        int ans = 0 ;
        for(int i = 0; i < N; i++)
        {
            switch (S[i])
            {
                case 'I':
                    x++;
                    break;
                case 'D':
                    x--;
                    break;
                default:
                    throw new Exception();
            }
            ans = Math.Max(ans, x);
        }
        Console.WriteLine(ans);
    }
}