#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    int a[1000] = {0};
    int guaidianCount = 0;

    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    for (int i = 1; i < n - 1; i++) {
        if (a[i] - a[i - 1] > 0 && a[i + 1] - a[i] < 0) {
            guaidianCount++;
        }
        if (a[i] - a[i - 1] < 0 && a[i + 1] - a[i] > 0) {
            guaidianCount++;
        }
    }
    cout << guaidianCount << endl;
    return 0;
}