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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
$n=trim(fgets(STDIN));
$p=explode(" ",trim(fgets(STDIN)));
$ans=0;
$a=$p[0];
$b=$p[1];
$i=2;
while($i<$n){
  if($a<$b&&$b<$p[$i]){
    ++$ans;
  }elseif($a>$b&&$b>$p[$i]){
    ++$ans;
  }
  $a=$b;
  $b=$p[$i];
  ++$i;
}
echo $ans;