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::cmp;

#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[allow(dead_code)]
fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn find_min(x: &[u64]) -> u64 {
    let mut min: u64 = x[0];
    let mut x_iter = x.iter();
    while let Some(i) = x_iter.next() {
        min = cmp::min(*i, min);
    }
    return min;
}

#[allow(dead_code)]
fn find_max(x: &[u64]) -> u64 {
    let mut max: u64 = x[0];
    let mut x_iter = x.iter();
    while let Some(i) = x_iter.next() {
        max = cmp::max(*i, max);
    }
    return max;
}

fn calc(v: &Vec<u64>) -> u64 {
    if v.len() == 1 {
        v[0]
    } else {
        let min: u64 = find_min(v);
        let vec: Vec<u64> = v.iter().map(|x| x - min).collect();
        let mut ans: u64 = min;

        let mut i: usize = 0;
        while i < vec.len() {
            let mut tmp: Vec<u64> = Vec::new();
            while i < vec.len() && vec[i] != 0 {
                tmp.push(vec[i]);
                i += 1;
            }
            i += 1;
            if tmp.len() > 0 {
                ans += calc(&tmp);
            }
        }
        ans
    }
}

fn main() {
    let _n: u64 = read();
    let h: Vec<u64> = read_vec();

    println!("{}", calc(&h));
}