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

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

fn read_vec2<T: std::str::FromStr>(n: usize) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

fn read_col<T: std::str::FromStr>(n: usize) -> Vec<T> {
    (0..n).map(|_| read()).collect()
}

fn grow(l: usize, r: usize, h: u32, hv: &Vec<u32>) -> u32 {
    let mut tmp: usize = 0;
    let mut min: u32 = 111;

    let mut ans: u32 = 0;

    if hv[l] > h {
        tmp = l;
        min = hv[l];
    }
    for i in (l + 1)..r {
        if hv[i - 1] > h && hv[i] <= h {
            ans += min - h + grow(tmp, i, min, hv);
        } else if hv[i] > h {
            if hv[i] < min {
                min = hv[i];
            }
            if hv[i - 1] <= h {
                tmp = i;
                min = hv[i];
            }
        }
    }
    if hv[r - 1] > h {
        ans += min - h + grow(tmp, r, min, hv);
    }
    ans
}

fn main() {
    let n: usize = read();
    let hv: Vec<u32> = read_vec();

    println!("{}", grow(0, n, 0, &hv));
}