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.Text;
using System.Linq;
using System.Collections;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using static System.Console;
using static System.Math;

namespace NotFounds
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve();
        }

        public void Solve()
        {
            MyInputStream cin = new MyInputStream();

            var N = cin.ReadInt();
            var max = 0;
            var x = 0;
            for (int i = 0; i < N; ++i)
            {
                if (Read() == 'I')
                    max = Max(++x, max);
                else
                    --x;
            }
            WriteLine(max);
        }
    }

    public static class MyExtensions
    {
        public static string Reverse(this string sourse)
        {
            char[] chrAry = sourse.ToCharArray();
            Array.Reverse(chrAry);
            return new string(chrAry);
        }
    }

    public class MyInputStream
    {
        private char separator = ' ';
        private Queue<string> inputStream;
        public MyInputStream(char separator = ' ')
        {
            this.separator = separator;
            inputStream = new Queue<string>();
        }

        public string Read()
        {
            if (inputStream.Count != 0) return inputStream.Dequeue();
            string[] tmp = Console.ReadLine().Split(separator);
            for (int i = 0; i < tmp.Length; i++)
            {
                inputStream.Enqueue(tmp[i]);
            }
            return inputStream.Dequeue();
        }
        public string ReadLine() => Console.ReadLine();
        public int ReadInt() => int.Parse(Read());
        public long ReadLong() => long.Parse(Read());
        public double ReadDouble() => double.Parse(Read());
    }

    public class Pair<T1, T2>
    {
        public T1 First;
        public T2 Second;
        public Pair() { First = default(T1); Second = default(T2); }
        public Pair(T1 f, T2 s) { First = f; Second = s; }
        public override string ToString() { return "(" + First + ", " + Second + ")"; }
        public override int GetHashCode() { return First.GetHashCode() ^ Second.GetHashCode(); }
        public override bool Equals(object obj)
        {
            if (ReferenceEquals(this, obj)) return true;
            else if (obj == null) return false;
            var tmp = obj as Pair<T1, T2>;
            return (object)tmp != null && First.Equals(tmp.First) && Second.Equals(tmp.Second);
        }
    }

    #region HashMap
    public class HashMap<K, V> : Dictionary<K, V>
    {
        public HashMap() : base() { }
        public HashMap(int cap) : base(cap) { }
        public HashMap(IDictionary<K, V> dictionary) : base(dictionary) { }
        new public V this[K i]
        {
            get
            {
                V v;
                return TryGetValue(i, out v) ? v : base[i] = default(V);
            }
            set { base[i] = value; }
        }
    }
    #endregion
}