#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <limits>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <complex>

using namespace std;

#define INF (INT_MAX/3)
#define PI (2*acos(0.0))
#define EPS (1e-8)

typedef long long ll;
typedef unsigned long long ull;

int main(){
  ios_base::sync_with_stdio(0);
  int N;
  cin >> N;
  vector<int> a(N);
  for(int i = 0; i < N; i++) cin >> a[i];

  int cnt = 0;
  for(int i = 2; i < N; i++){
    if(a[i] != a[i-1] && a[i-1] != a[i-2] && a[i] != a[i-2]){
      if(a[i-1] > a[i] && a[i-1] > a[i-2]) cnt++;
      if(a[i-1] < a[i] && a[i-1] < a[i-2]) cnt++;
    }
  }
  cout << cnt << endl;
  return 0;
}