#include<bits/stdc++.h>
using namespace std;
int n,a[25],num; 
int main(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>a[i];
	for(int i=2;i<n;i++) 
	    if((a[i]>=a[i-1]&&a[i]<=a[i+1])||(a[i]>=a[i+1]&&a[i]<=a[i-1])) num++;
	cout<<num;
	return 0;
}