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 <bits/stdc++.h>

#define PI 3.14159265359
#define INF 1e9
#define LINF 1e18
#define IMOD 1000000007 
#define irep(i,n) for(int i = 0; i < (int)(n); i++)
#define irep2(i,a,n) for(int i = (int)(a); i <= (int)(n); i++)
#define lrep(i,n) for(long long  i = 0; i < (long long)(n); i++)
#define lrep2(i,a,n) for(long long i = (long long)(a); i <= (long long)(n); i++)

#define irrep(i,n) for(int i = (int)(n); i > -1; i--)
#define irrep2(i,a,n) for(int i = (int)(n); i >= (int)(a); i--)

typedef long long ll;
typedef std::vector<char> v_char;
typedef std::vector<std::vector<char> > v2_char;
typedef std::vector<double> v_double;
typedef std::vector<std::vector<double> > v2_double;
typedef std::vector<int> v_int;
typedef std::vector<std::vector<int> > v2_int;
typedef std::vector<ll> v_ll;
typedef std::vector<std::vector<ll> > v2_ll;
typedef std::vector<std::string> v_string;
typedef std::vector<std::vector<std::string> > v2_string;
typedef std::vector<bool> v_bool;
typedef std::vector<std::vector<bool> > v2_bool;
typedef std::pair<ll, ll> pll;
typedef std::pair<int, int> pii;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

using namespace std; 

int main(void)
{
    int n; cin >> n;
    string s; cin >> s;
    
    int ans = 0, x = 0;
    irep(i, n) {
        if(s[i] == 'I') {
            x++;
        } else {
            x--;
        }
        ans = max(x, ans); 
    }
    cout << ans << endl;
    return 0;
}
/** atcoder **/