#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)

int main(){
  int n;
  cin>>n;
  int a[n];
  rep(i,n) cin>>a[i];
  int cnt=0;
  rep(i,n-2){
    if(a[i] != a[i+1] && a[i] != a[i+2] && a[i+1] != a[i+2]){
      if(max(max(a[i],a[i+1]),a[i+2]) == a[i+1] || min(min(a[i],a[i+1]),a[i+2]) == a[i+1]){
        cnt++;
      }
    }
  }
  cout<<cnt<<endl;
  return 0;
}