#include <bits/stdc++.h>
#define rep(i,l,n) for(int i=l;i<n;i++)
#define rer(i,l,n) for(int i=l;i<=n;i++)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
using namespace std;
typedef long long lint;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

int main(){
	int n,ans=0;
	cin>>n;
	vi a(n);
	rep(i,0,n) cin>>a[i];
	rep(i,0,n-2){
		if((max(a[i],max(a[i+1],a[i+2]))==a[i+1]||min(a[i],min(a[i+1],a[i+2]))==a[i+1])&&a[i]!=a[i+2]&&a[i]!=a[i+1]) ans++;
	}
	o(ans);
}