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::stdin;

fn main() {
    let mut s = String::new();
    stdin().read_line(&mut s).ok();
    let n: usize = s.trim().parse().ok().unwrap();
    s = String::new();
    stdin().read_line(&mut s).ok();
    let hs: Vec<u32> = s.trim().split_whitespace().map(|token| token.parse().ok().unwrap()).collect();

    let mut sum = 0;
    let max = *(hs.iter().max().unwrap());
    for m in (1..max + 1).rev() {
        let mut tmp = 0;
        for i in 0..n {
            if hs[i] >= m && (i == 0 || hs[i - 1] < m) {
                    tmp = tmp + 1;
            }
        }
        sum = sum + tmp;
    }
    print!("{}", sum);
}