#include <iostream>
#include <vector>
using namespace std;
int main(){
    int n;cin>>n;
    vector<int> a(n);
    int ans = 0;
    for(int i = 0; n > i; i++)cin>>a[i];
    for(int i = 2; n > i; i++){
        if(a[i-2] != a[i-1] && a[i-1] != a[i] && a[i] != a[i-2] && !((a[i] > a[i-1] && a[i-1] > a[i-2]) || (a[i-2] > a[i-1] && a[i-1] > a[i]))){
            ans++;
        }
    }
    cout << ans << endl;
    
}