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 main() {
    use std::io::Read;
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut iter = buf.split_whitespace();
    
    let n: usize = iter.next().unwrap().parse().unwrap();
    let h: Vec<u64> = (&mut iter).take(n).map(|x| x.parse().unwrap()).collect();
    
    println!("{}", count(&h, 0));
}

fn count(h: &[u64], base: u64) -> u64 {
    let &m = h.iter().min().unwrap();
    let mut cnt = m - base;
    for t in split_series(h, m) {
        cnt += count(&t, m);
    }
    cnt
}

#[allow(dead_code)]
fn split_series<T: Clone + Eq>(series: &[T], sep: T) -> Vec<Vec<T>> {
    let mut l = 0;
    let mut ret = vec![];
    for r in 0..series.len() {
        if series[r] == sep {
            if l != r {
                ret.push(series[l..r].to_vec());
            }
            l = r + 1;
        }
    }
    if l != series.len() {
        ret.push(series[l..series.len()].to_vec());
    }
    ret
}