#include <iostream>
#include <list>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdint.h>
using namespace std;

using uint = unsigned int;
using ll = long long;

#define CIN( LL , A ) LL A; cin >> A 
#define GETLINE( A ) string A; getline( cin , A ) 

int main()
{

  CIN( ll , N );
  ll A;
  ll B;
  ll C;
  ll answer = 0;
  
  for( ll i = 0 ; i < N ; i++ ){

    if( i == 0 ){

      cin >> B;

    } else if( i == 1 ){

      cin >> C;

    } else {

      A = B;
      B = C;
      cin >> C;

      if( A != B && B != C && C != A ){

	if( ( !( A < B && B < C ) ) && ( !( A > B && B > C ) ) ){

	  answer++;

	}

      }
      
    }
    
  }

  cout << answer << endl;
  return 0;

}