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 Rust (1.15.1) (judge verdict: Accepted)

fn main() {
    let _n: usize = read();
    let s: String = read();
    let mut count = 0;
    let mut ans = 0;
    for c in s.chars() {
        if c == 'I' {
            count += 1;
        } else if c == 'D' {
            count -= 1;
        }
        ans = std::cmp::max(count, ans)
    }
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    use std::io::prelude::*;

    let stdin = std::io::stdin();
    let s: String = stdin
        .lock()
        .bytes()
        .map(|b| b.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    s.parse().ok().unwrap()
}