Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io;

fn main() {
    let stdin = io::stdin();
    let mut line1 = String::new();
    let _ = stdin.read_line(&mut line1);
    let mut line1 = line1.trim_right().split_whitespace();

    let _ = line1.next().unwrap().parse::<usize>().unwrap();

    let mut line2 = String::new();
    let _ = stdin.read_line(&mut line2);
    let line2 = line2.trim_right().split_whitespace();

    let mut flowers = line2.map(|s| s.parse::<usize>().unwrap()).collect::<Vec<usize>>();

    let mut n = 0;
    loop {
        let mut now = false;
        let mut flag = false;
        for flower in flowers.iter_mut() {
            let degradable = is_degradable(*flower);
            if !now && degradable {
                n += 1;
            }

            if degradable {
                flag = true;
                *flower = *flower - 1;
            }

            now = degradable;
        }

        if !flag { break; }
    }
    println!("{}", n);
}



fn is_degradable(num: usize) -> bool {
    if num > 0 {
        true
    } else {
        false
    }
}