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::stdin;

fn doit(arr: &mut Vec<usize>) -> usize {
    // Split by zero
    arr.split_mut(|&a| a == 0).map(|a| {
        // Get minimum height
        let mut min = None;
        for &h in a.iter() {
            min = match min {
                None => Some(h),
                Some(x) if h < x => Some(h),
                _ => min,
            };
        }

        // Each values subtract by the minimum height
        if let Some(x) = min {
            for h in a.iter_mut() {
                *h -= x;
            }
            // Doit!!
            x + doit(a.to_vec().as_mut())
        } else {
            0
        }
    }).sum()
}

fn main () {
    let mut n = String::new();
    stdin().read_line(&mut n).unwrap();
    let mut harr = String::new();
    stdin().read_line(&mut harr).unwrap();
    println!("{}", doit(&mut harr.trim().split_whitespace().flat_map(str::parse).collect()));
}