#include <bits/stdc++.h>

using namespace std;

int main()
{
  int N, A[100];
  cin >> N;
  for(int i = 0; i < N; i++) {
    cin >> A[i];
  }

  int ret = 0;
  for(int i = 1; i < N - 1; i++) {
    int j = i - 1, k = i + 1;
    if(A[i] != A[j] && A[j] != A[k] && A[i] != A[k] && (min({A[i], A[j], A[k]}) == A[i] || max(
      {A[i], A[j], A[k]}) == A[i])) {
      ++ret;
    }
  }
  cout << ret << endl;
}