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 (Clang 3.8.0) (judge verdict: Accepted)

#include<stdio.h>
int main () {
	long long int n, i, count = 0;
	scanf("%lld", &n);
	long long int arr[n];
	for (i = 0; i < n; i++) {
		scanf("%lld", &arr[i]);
//		printf("%lld\n", arr[i]);
	}
	for (i = 1; i < n - 1; i++) {
		if (arr[i] < arr[i + 1] && arr[i] > arr[i - 1]) {
			count++;
		}
		if (arr[i] > arr[i + 1] && arr[i] < arr[i - 1]) {
			count++;
		}
	}
	printf("%lld\n", count);

	return 0;
}