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

// Scan n
fscanf(STDIN, "%d", $n);
$s = fgets(STDIN);
$a = array_slice(explode(" ", $s), 0, $n);
foreach (range(0, $n - 1) as $i) {
    $a[$i] = (int)$a[$i];
}

$res = $a[0];
$last_slump = $a[0];
$last_peak = $a[0];
for ($i = 1; $i <= $n - 2; $i++) {
    if ($a[$i - 1] <= $a[$i] && $a[$i] > $a[$i + 1]) {
        $res += $a[$i] - $last_slump;
        $last_peak = $a[$i];
    }
    if ($a[$i - 1] >= $a[$i] && $a[$i] < $a[$i + 1]) {
        $last_slump = $a[$i];
    }
}
if ($n > 1 && $a[$n - 1] > $a[$n - 2]) {
    $res += ($a[$n - 1] - $last_slump);
}

echo "$res";