#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

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