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 Java7 (OpenJDK 1.7.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {

	public static int min2(int a, int b, int c) {
		int min = Math.min(a, b);
		int min2 = Math.min(b, c);
		int min3 = Math.min(a, c);
		if (min == min2)
			return min3;
		else if (min == min3)
			return min2;
		return min;
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[] = new int[n];
		for (int i = 0; i < n; ++i)
			p[i] = sc.nextInt();
		sc.close();
		int cnt = 0;
		for (int i = 1; i < n - 1; ++i) {
			int min2 = min2(p[i - 1], p[i], p[i + 1]);
			if (p[i] == min2)
				++cnt;
		}
		System.out.println(cnt);
	}

}