#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main() {
	int n;
	cin >> n;
	int ans = 0;
	int data[n];
	REP(i,n){
		cin >> data[i];
	}
	REP(i,n-2){
		if(data[i+1] > data[i] && data[i+1] > data[i+2] && !(data[i]==data[i+2])) ans += 1;
		if(data[i+1] < data[i] && data[i+1] < data[i+2] && !(data[i]==data[i+2])) ans += 1;
	}
	cout << ans << endl;
	return 0;
}