#include <iostream>
#include <random>
#include <algorithm>
#define INF 1000000000
using namespace std;
// #define int long long



signed main(){
  int N;
  int A[1000];
  cin >> N;
  for(int i=0;i<N;i++){
    cin >> A[i];
  }
  int c =0;
  for(int i=0;i<(N-2);i++){
    if(
      (
        (
          (A[i+1]<A[i])+
          (A[i+1]<A[i+2]))!=1
        ) /**/
        && A[i]!=A[i+1]
        && A[i+1]!=A[i+2]
        && A[i]!=A[i+2]
    )c++;
  }
  cout << c << endl;
}