#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n, ans = 0;
    vector<int> as;
    cin >> n;
    for (int i = 0, a; i < n && cin >> a; i++)
        as.push_back(a);
    for (int i = 0; i < n-2; i++) {
        if (!(as[i] <= as[i+1] && as[i+1] <= as[i+2] || as[i+2] <= as[i+1] && as[i+1] <= as[i] || as[i] == as[i+2]))
            ans++;
    }
    cout << ans << endl;
    return 0;
}