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)

#![allow(non_snake_case)]

fn read_line() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

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


fn print_vec(vec: &Vec<i32>) {
    for i in 0..vec.len()-1 {
        print!("{} ", vec[i]);
    }
    println!("{}", vec[vec.len()-1]);
}

fn main() {
    let N: usize = read_line().parse().unwrap();
    let mut h: Vec<i32> = read_vec();
    h.insert(0, 0);
    h.push(0);
    let mut ans = 0;
    while h.iter().any(|&x| x > 0) {
        let first = h.iter().position(|&x| x != 0).unwrap();
        let second = first + h[first..].iter().position(|&x| x == 0).unwrap();
        for i in first..second {
            h[i] -= 1;
        }
        ans += 1;
    }
    println!("{}", ans);
}