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)

fn main() {
    let mut buf = String::new();
    let handle = std::io::stdin();
    let n: usize = {
        handle.read_line(&mut buf).unwrap();
        let tmp = buf.trim().parse().unwrap();
        buf.clear();
        tmp
    };
    let mut hs: Vec<usize> = {
        handle.read_line(&mut buf).unwrap();
        let tmp = buf
            .trim()
            .split_whitespace()
            .map(|a| a.parse().unwrap())
            .collect();
        buf.clear();
        tmp
    };
    let mut left = hs.iter().filter(|&&a| a != 0).count();
    let mut count = 0;
    loop {
        if left == 0 {
            break;
        }
        let (index, length) = find_tops(&hs);
        for i in index..index + length {
            hs[i] -= 1;
            if hs[i] == 0 {
                left -= 1;
            }
        }
        count += 1;
    }
    println!("{}", count);
}
fn find_tops(hs: &Vec<usize>) -> (usize, usize) {
    let mut i = 0;
    let mut length = 1;
    let mut start = 0;
    loop {
        if i == hs.len() {
            break;
        }
        let next = hs.get(i + 1);
        match next {
            Some(&h) => {
                if hs[i] < h {
                    i += 1;
                    start = i;
                    length = 1;
                    continue;
                } else if hs[i] == h {
                    i += 1;
                    length += 1;
                } else if hs[i] > h {
                    break;
                }
            }
            None => { break; }
        }
    }
    (start, length)
}