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::vec::Vec;
use std::cmp::*;

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 main() {
    let n: usize = read();
    let mut h: Vec<usize> = read_vec();

    let mut ans = 0;
    while !check_all_zero(&h) {
      let mut l = n;
      let mut r = 0;

      for i in 0..n {
        if h[i] > 0 {
          l = i;
          break;
        }
      }

      for j in l..n {
        if h[j] == 0 {
          r = j;
          break;
        } else if j == n-1 {
          r = n;
          break;
        }
      }

      for k in l..r {
        h[k] -= 1;
      }
      ans += 1;
    }

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


fn check_all_zero(h: &Vec<usize>) -> bool {
  for i in 0..h.len() {
    if h[i] > 0 {
      return false;
    }
  }

  return true;
}