#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> v;
    int count{0};
    for (int i = 0; i < n; ++i) {
        int tmp;
        cin >> tmp;
        v.push_back(tmp);
    }
    for (int j = 0; j < (n - 2); ++j) {
        auto itr = v.begin() + j;
        if (v.at(j) != v.at(j+1) && v.at(j+1) != v.at(j+2) && v.at(j+2) != v.at(j)) {
            auto p = minmax_element(itr, itr + 2);
            if (v.at(j + 1) == *p.first || v.at(j + 1) == *p.second) count++;
        }
    }
    cout << count << endl;
    return 0;
}