#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(){


  int n,tmp;
  cin >> n;
  tmp = 0;
  vector<int> v;
  for (int i = 0; i < n; i++) {
    int a;
    cin >> a;
    v.push_back(a);
  }

  //昇順、降順を作り比較
  for (int i = 0; i < n - 2; i++) {
    vector<int> org,down,up;
    org = {v[i],v[i+1],v[i+2]};
    down = {v[i],v[i+1],v[i+2]};
    up = {v[i],v[i+1],v[i+2]};
    sort(down.begin(),down.end(),greater<int>());
    sort(up.begin(),up.end());
    if (org != down && org != up) {
      tmp++;
    }
  }
  cout << tmp << "\n";


  return 0;
}