#include <bits/stdc++.h>
using namespace std;

signed main(){
  int N; cin >> N;
  vector< int > A( N );
  for( int i = 0; i < N; ++i )
    cin >> A[ i ];
  int ans = 0;
  for( int i = 0; i + 3 <= N; ++i ){
    if( A[ i ] == A[ i + 1 ] or A[ i + 1 ] == A[ i + 2 ] or A[ i ] == A[ i + 2 ] )
      continue;
    if( max( { A[ i ], A[ i + 1 ], A[ i + 2 ] } ) == A[ i + 1 ] )
      ++ans;
    if( min( { A[ i ], A[ i + 1 ], A[ i + 2 ] } ) == A[ i + 1 ] )
      ++ans;
  }
  cout << ans << endl;
  return 0;
}