#include <iostream>
#include <vector>

int main() {
    int n;
    int st = 0;
    int c = 0;
    std::vector<int> a(100, 0);
    std::cin >> n;
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }
    for (int i = 0; i < n - 1; i++) {
        int new_st = a[i + 1] - a[i];
        if (a[i - 1] != a[i + 1] && st * new_st < 0) {
            c++;
        }
        st = new_st;
    }
    std::cout << c << std::endl;
}