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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;

public class AtCoderB
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        int[] ps = new int[n];
        {
            var line = Console.ReadLine();
            var words = line.Split(' ');
            for(int i = 0; i < n; i++){
                ps[i] = int.Parse(words[i]);
            }
        }

        int answer = 0;
        for(int i = 1; i < n - 1; i++)
        {
            int a = ps[i - 1];
            int b = ps[i];
            int c = ps[i + 1];
            if((a < b && b < c)|| (a > b && b > c))
            {
                answer++;
            }
        }

        Console.WriteLine(answer);
    }
}