#include <iostream>
#include <list>
using namespace std;
 
int main(){
	int N;
	cin >> N;
	int bamboo[N];
	for(int i = 0; i < N; i++){
		cin >> bamboo[i];
	}
	int ans = 0;
	for(int i = 0; i < N - 2; i++){
		if(bamboo[i] != bamboo[i + 1] && bamboo[i] != bamboo[i + 2] && bamboo[i + 1] != bamboo[i + 2] && !((bamboo[i] < bamboo[i + 1] && bamboo[i + 1] < bamboo[i + 2]) || (bamboo[i] > bamboo[i + 1] && bamboo[i + 1] > bamboo[i + 2]))){
			ans++;
		}
	}
	cout << ans << endl;
}