#include<bits/stdc++.h>
using namespace std;

const long long INF = 1LL << 60;
#define MOD 1000000007;

typedef long long ll;

#define writeln(n) cout<<n<<endl;

typedef pair<float, float> P;

typedef pair<string, int> Psi;


int d[110];
int main() {


	int n;
	cin>>n;

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

	int cnt=0;
	for(int i=1; i<n-1; i++){
		int mi = min(d[i-1],d[i]);
		int ma = max(d[i-1],d[i]);

		mi = min(mi,d[i+1]);
		ma = max(ma,d[i+1]);

		if((mi ==d[i] || ma ==d[i]) && d[i-1] != d[i] && d[i] != d[i+1] && d[i-1] !=d[i+1]){
			cnt++;

/*			cout<<d[i-1]<<" "<<d[i]<<" "<<d[i+1]<<endl;*/
		}
	}

	writeln(cnt);




}