#include<iostream>
using namespace std;
main(){
	int n,a[100],c=0;cin>>n;
	for(int i=0;i<n;i++)cin>>a[i];
	for(int i=0;i<n-2;i++)
	{
		if(a[i]==a[i+1]||a[i+1]==a[i+2]||a[i]==a[i+2])continue;
		if(a[i+1]>a[i]&&a[i+1]>a[i+2])c++;
		else if(a[i+1]<a[i]&&a[i+1]<a[i+2])c++;
	}
	cout<<c<<endl;
}