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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
// 標準入力から取得
class Scanner {
    private $arr = [];
    private $count = 0;
    private $pointer = 0;
    public function next() {
        if($this->pointer >= $this->count) {
            $str = trim(fgets(STDIN));
            $this->arr = explode(' ', $str);
            $this->count = count($this->arr);
            $this->pointer = 0;
        }
        $result = $this->arr[$this->pointer];
        $this->pointer++;
        return $result;
    }
    public function hasNext() {
        return $this->pointer < $this->count;
    }
    public function nextInt() {
        return (int)$this->next();
    }
    public function nextDouble() {
        return (double)$this->next();
    }
}
 
class SubmitAnswer {
    public static function println($answer = "") {
        echo $answer . PHP_EOL;
    }
}
 
$sc = new Scanner();
$n = $sc->nextInt();
$array = [];
$maxNumber = 0;
$count = 0;
$height = 0;
//8
//4 23 75 0 23 96 50 100

for($i=0;$i<$n;$i++){
  $array[$i] = $sc->nextInt();
  if($array[$i] > $maxNumber){
      $maxNumber = $array[$i];
  }
}

for($i=0;$i<$maxNumber;$i++){
    $height = 0;
    for ($j=0;$j<$n;$j++) {
        if($array[$j] > 0){
            if($height == 0){
                $height = 1;
                $count++;
            }
            $array[$j]--;
        }
        if($array[$j] == 0){
            if($height == 1){
                $height = 0;
            }
        }
    }    
}

$answer = $count;

SubmitAnswer::println("$answer");