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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
fscanf(STDIN, "%d", $N);
$h = array_map("intval", explode(" ", trim(fgets(STDIN))));
$ans = 0;
while(array_sum($h) !== 0) {
    $l = $r = null;
    foreach ($h as $k => $v) {
        if (is_null($l)) {
            if ($v !== 0) {
                $l = $k;
                $mmin = $v;
            }
        } else {
            // echo "B" . PHP_EOL;
            if (is_null($r)) {
                if ($v === 0) {
                    $r = $k - 1;
                    break;
                }
            } else {
            }
            // echo "C" . PHP_EOL;
            $mmin = min($mmin, $v);
            // printf("%d %d\n", $k, $mmin);
        }
    }
    if (is_null($r)) {
        $r = $N - 1;        
    }
    // printf("%d %d %d", $l, $r, $mmin);
    for ($i = $l; $i <= $r; $i++) {
        $h[$i] -= $mmin;
    }
    $ans += $mmin;
}
echo $ans;