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: Wrong Answer)

#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); i++)
#define prtd(var, i) cout << fixed << setprecision(i) << var << endl;
#define ll long long
using namespace std;
#define INF 100000

int main(){
    int n; cin >> n;
    string s;
    cin >> s;
    int cnt = 0;
    int MAX = -1000;
    rep(i, n){
        if(s[i] == 'D') cnt--;
        else if(s[i] == 'I') cnt++;
        MAX = max(MAX, cnt);
    }
   cout << MAX << endl;
}