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;

namespace abc132B
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            string[] str = Console.ReadLine().Split();
            int[] stl = new int[N];
            for(int m = 0; m < N; m++)
            {
                stl[m] = int.Parse(str[m]);
            }
            int Ans = 0;
            for(int i = 0; i < N-2; i++)
            {
                if (stl[i] < stl[i + 1] && stl[i + 1] < stl[i + 2])
                    Ans = Ans + 1;
                else if (stl[i] > stl[i + 1] && stl[i + 1] > stl[i + 2])
                    Ans = Ans + 1;
            }
            Console.WriteLine(Ans);
        }
    }
}