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)

use std::io;
use std::cmp::max;

fn main (){
    let _ = get_line();
    let nums = get_line();
    let mut sim = nums.chars().scan(0, |acc, n| {
        // this feels totally weird. TOTALLY
        match n {
            'D' => { *acc = *acc-1; Some(*acc) }
            'I' => { *acc = *acc+1; Some(*acc) }
            _ => panic!("die")
        }
    });
    // maximum . catMaybes
    let mut ans = 0;
    while let Some(n) = sim.next(){
        ans = max(ans,n);
    }
    println!("{}",ans);
}

fn get_line() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).expect("orders");
    buf.trim().to_string()
}