#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
using namespace std;
#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,P> Q;
 
const int inf = (int)1e9; 
 
ll gcd(ll a, ll b) {
	if (b > a) {
		ll tmp = b;
		b = a;
		a = tmp;
	}
	if (a%b == 0)return b;
	else return gcd(b, a%b);
}



int main(void){
	int n;
	cin>>n;
	vector<int>a(n);
	for(int i=0;i<n;i++)cin>>a[i];
	int ans = 0;
	for(int i=0;i<n-2;i++){
		if(a[i]<=a[i+1]&&a[i+1]<=a[i+2])continue;
		if((a[i]>=a[i+1])&&(a[i+1]>=a[i+2]))continue;
		if(a[i]==a[i+2])continue;
		ans++;
	}
	cout<<ans<<endl;
	return 0;
}