// Enjoy your stay.

#include <bits/stdc++.h>

#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define all(x) (x).begin(),(x).end()
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define ite iterator
#define mp make_pair
#define mt make_tuple
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define sec second
#define sz(x) ((int)(x).size())

using namespace std;

typedef istringstream iss;
typedef long long ll;
typedef pair<ll,ll> pi;
typedef stringstream sst;
typedef vector<ll> vi;



int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	
	int n,a[111];
	cin>>n;
	rep(i,n)cin>>a[i];
	int ans = 0;
	rep(i,n-2){
		int j = i+1, k = i+2;
		if(a[j] > a[i] && a[j] > a[k] && a[i] != a[k]
		|| a[j] < a[i] && a[j] < a[k] && a[i] != a[k]) ans++;
	}
	cout<<ans<<endl;
}