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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<string>
#include<iostream>
#include<algorithm>
#include<set>
#include<math.h>
#include<vector>
#include<sstream>
#include<queue>
#include<functional>
#include<bitset>
#include<cstdio>
#include<iomanip>
using namespace std;
#define REP(i,n) for(int i=0;i < n; i++)
#define RREP(i,n) for(int i=n-1;i >=0; i--)
#define p(a) (a) * (a)
#define p2(a,b) p((a) - (b)) 

#define MAX 100002

int main() {
	int x = 0, n,m =0;
	string s;
	cin >> n >> s;
	for (int i = 0; i < n; i++) {
		if (s[i] == 'I') {
			x++;
		}
		else {
			x--;
		}
		m = max(m, x);
	}
	cout << m << endl;
	return 0;
}