#include <stdio.h>
#include <algorithm>
#include <deque>
using namespace std;
using ll = long long;

//116
int main() {
	int n, a[100], count = 0;
	scanf("%d", &n);
	for (int i = 0; i < n; i++)
		scanf("%d", a + i);
	for (int i = 1; i < (n - 1); i++)
		if ((a[i - 1] != a[i] && a[i] != a[i + 1] && a[i - 1] != a[i + 1]) && (
			(int)(a[i - 1] > a[i]) + (int)(a[i - 1] > a[i + 1]) == 1 || 
			(int)(a[i + 1] > a[i]) + (int)(a[i + 1] > a[i - 1]) == 1))
			count++;
	printf("%d\n", count);
}