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;
use std::io::prelude::*;

fn water(h: &mut [usize]) -> usize {
    let min = *h.iter().min().unwrap();
    for h in h.iter_mut() {
        *h -= min;
    }
    return min;
}

fn main () {
    let mut stdin = io::stdin();
    let mut buf = String::new();
    let _ = stdin.read_to_string(&mut buf);
    let mut iter = buf.split_whitespace();
    let n: usize = iter.next().unwrap().parse().unwrap();
    let mut h: Vec<usize> = (0..n).map(|_| iter.next().unwrap().parse().unwrap()).collect();

    let mut ans: usize = 0;
    while let Some(l) = h.iter().position(|&x| x > 0) {
        let r = h[l..].iter().position(|&x| x == 0).map(|x| x + l).unwrap_or(n);
        ans += water(&mut h[l..r]);
    }
    println!("{}", ans);
    return;
}