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 Perl (v5.18.2) (judge verdict: Accepted)

#!/usr/bin/perl

use strict;
use warnings;

my $n = int(<STDIN>);
my @p = split(/\s+/, <STDIN>);
for (my $i = 0; $i < @p; $i++) {
	$p[$i] = int($p[$i]);
}

my $count = 0;

for (my $i = 1; $i < $n - 1; $i++) {
	my @d = ($p[$i-1], $p[$i], $p[$i+1]);
	my @dd = sort { $a <=> $b } @d;
	if ($dd[1] == $p[$i]) { $count++; }
}

print "$count\n";