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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

//intのオーバーフローに気をつけろ,AGCはだいたいlongにしておけ
//毎回余りを求めることでオーバーフローしなくなる
//nextLineよりnextだ
//charは''で囲うんだぞ
//読み込みは先に全部やっておけ
//for文を回す回数に気をつけろ
	//for文は10^3の三重はTLE,10^5の二重はTLE

import java.util.Scanner;

public class Main {

	public static void main(String args[]) throws InterruptedException {
		    Scanner sc = new Scanner(System.in);
		    
		    int s = sc.nextInt();
		    String id = sc.next();
		    int max = 0;
		    int tmp = 0;
		    
		    for(int i = 0; i < s; i++) {
		    	if(id.charAt(i) == 'I') {
		    		tmp++;
		    		if(tmp > max) {
		    			max = tmp;
		    		}
		    	}else {
		    		tmp--;
		    	}
		    }
		    System.out.println(max);
		    sc.close(); }

	public static void saiki(int a, String b) {
		//再帰コーディングのお手本

		if(a == 0) {
			System.out.println(b);
		}else {
			for(char ch = 'a'; ch <= 'c'; ch++) {
				saiki(a-1,b + ch);
			}
		}
	}

	public static  int gcd(int a, int b) {
	    if (a < b) {
	        int tmp = a;
	        a = b;
	        b = tmp;
	    }

	    int r = -1;
	    while (r != 0) {
	        r = a % b;
	        a = b;
	        b = r;
	    }

	    return a;
	}
}