#include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define ALL(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
const int INF=1e9;
int main(){
      int n;
      int a[100],ans=0;
      cin>>n;
      REP(i,n)cin>>a[i];
      for(int i=1;i<n-1;i++){
            if(a[i]==a[i-1]||a[i]==a[i+1]||a[i-1]==a[i+1])continue;
            if(a[i]>a[i-1]&&a[i]>a[i+1]){
                  //cout<<a[i-1]<<" "<<a[i]<<" "<<a[i+1]<<endl;
                  ans++;
            }else if(a[i]<a[i-1]&&a[i]<a[i+1]){
                  //cout<<a[i-1]<<" "<<a[i]<<" "<<a[i+1]<<endl;
                  ans++;
            }
      }
      cout<<ans<<endl;
}