Problem:
Score : 200 points

Problem Statement

We have a permutation p = {p_1,\ p_2,\ ...,\ p_n} of {1,\ 2,\ ...,\ n}.

Print the number of elements p_i (1 < i < n) that satisfy the following condition:

p_i is the second smallest number among the three numbers p_{i - 1}, p_i, and p_{i + 1}.

Constraints

All values in input are integers.

3 \leq n \leq 20

p is a permutation of {1,\ 2,\ ...,\ n}.

Input

Input is given from Standard Input in the following format:

n
p_1 p_2 ... p_n

Output

Print the number of elements p_i (1 < i < n) that satisfy the condition.

Sample Input 1

5
1 3 5 4 2

Sample Output 1

2

p_2 = 3 is the second smallest number among p_1 = 1, p_2 = 3, and p_3 = 5. Also, p_4 = 4 is the second smallest number among p_3 = 5, p_4 = 4, and p_5 = 2. These two elements satisfy the condition.

Sample Input 2

9
9 6 3 2 5 8 7 4 1

Sample Output 2

5

Solution in PHP (5.6.30) (judge verdict: Wrong Answer)

<?php

$stdin = fopen('php://stdin', "r");
fscanf($stdin, "%d", $n);
$arr = explode(' ', fgets($stdin));

$c = 0;
for ($i=1; $i<$n-1; $i++) {
    $a = [];
    $a [] = $arr[$i-1];
    $a [] = $arr[$i];
    $a [] = $arr[$i+1];
    sort($a);
    if ($a[1] == $arr[$i] && $a[0] != $a[1] && $a[1] != $a[2]) {
        $c++;
    }
}

echo "$c\n";