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 check_garden(h: &mut Vec<u32>, begin: usize, end: usize) -> u32 {
    if begin == end {
        return 0;
    }

    let grow = *h[begin..end].iter().min().unwrap();
    for i in h[begin..end].iter_mut() {
        *i -= grow;
    }
    let mut ans = grow;
    let mut i = begin;
    while i < end {
        if h[i] != 0 {
            for j in (i + 1)..end {
                if h[j] == 0 {
                    ans += check_garden(h, i, j);
                    i = j;
                    break;
                }
            }
            return ans + check_garden(h, i, end);
        }
        i += 1;
    }
    ans
}

fn c_grand_garden() {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).expect("input error");
    let n = input.trim_right().parse::<usize>().expect("parse error");
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).expect("input error");
    let mut h : Vec<u32> = input.split_whitespace()
        .filter_map(|s| s.parse::<u32>().ok())
        .collect();

    println!("{}", check_garden(&mut h, 0, n));
}

fn main() {
    c_grand_garden();
}