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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int n =sc.nextInt();
    String S = sc.next();
    char[]ss = S.toCharArray();
    ArrayList<Integer>ans  = new ArrayList<>();

    int a = 0;
    ans.add(a);
    for(int i=0; i<n; i++) {
    	if(ss[i] == 'I') {
    	a += 1;
    	ans.add(a);
    	}else {
    	a -= 1;
    	ans.add(a);
    	}
    }
    	Collections.sort(ans,Collections.reverseOrder());   		

    	System.out.println(ans.get(0));
    }
}