#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const double eps = 1e-6;
const int MAXN = 1e5 + 10;
const int MAXM = 1e6 + 10;
const long long mod = 1e9 + 7;
int a[1010];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", &a[i]);
  int ans = 0;
  for (int i = 1; i < n - 1; i++) {
    if (a[i] > a[i - 1] && a[i] > a[i + 1]) ans++;
    if (a[i] < a[i - 1] && a[i] < a[i + 1]) ans++;
  }
  printf("%d\n", ans);
  return 0;
}
