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::prelude::*;

fn input<T>() -> T
where
    T: std::str::FromStr,
{
    let stdin = std::io::stdin();
    let token = stdin
        .lock()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect::<String>();
    token.parse().ok().unwrap()
}

fn main() {
    let n = input::<i64>();
    let h = (0..n).map(|_| input()).collect::<Vec<i64>>();

    let mut ans = 0;
    let mut hh = vec![0; n as usize];
    loop {
        let mut l = -1;
        let mut r = -1;
        for i in 0..n {
            if l < 0 && hh[i as usize] < h[i as usize] {
                l = i;
                r = i;
            } else if l < 0 {
                continue;
            } else if l >= 0 && hh[i as usize] < h[i as usize] {
                r += 1;
            } else {
                break;
            }
        }

        if l == -1 {
            break;
        }

        if r >= n {
            r = r - 1;
        }
        ans += 1;
        for i in l..r + 1 {
            hh[i as usize] += 1;
        }
    }

    println!("{}", ans);
}