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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int[] p = new int[sc.nextInt()];

    for(int pIdx=0;pIdx<p.length;pIdx++){
      p[pIdx]=sc.nextInt();
    }

    int count=0;
    for(int pIdx = 1;pIdx<p.length-1;pIdx++){
      if(isMatch(p[pIdx-1],p[pIdx],p[pIdx+1]))count++;
    }
    System.out.println(count);
  }

  static boolean isMatch(int pm1, int p0, int pp1) {
    if(p0 < pm1 && p0 < pp1) return false;
    return !(p0 > pm1 && p0 > pp1);
  }
}