#include<iostream>
#include<vector>
using namespace std;

int main(){
	int n;
	cin >> n;

	vector<int> v(n);
	for(int i = 0; i < n; i++){
		cin >> v[i];
	}

	int cnt = 0;
	for(int i = 0; i < n-2; i++){
		if(v[i] == v[i+1] || v[i] == v[i+2] || v[i+1] == v[i+2]) continue;
		if(v[i+1] > v[i] && v[i+1] > v[i+2]) cnt++;
		if(v[i+1] < v[i] && v[i+1] < v[i+2]) cnt++;
	}
	cout << cnt << endl;
}