#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n);
  REP (i, n) cin >> a[i];

  int ret = 0;
  for (int i = 0; i + 2 < n; i++) {
    if (a[i] == a[i+1] || a[i] == a[i+2] || a[i+1] == a[i+2])
      continue;
    int x = max({a[i], a[i+1], a[i+2]});
    int y = min({a[i], a[i+1], a[i+2]});
    if (a[i+1] == x || a[i+1] == y)
      ++ret;
  }
  cout << ret << endl;
  
  return 0;
}