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#include <bits/stdc++.h>

using namespace std;

vector<int> vec;

int Solve();

int main() {
    int sz;
    cin >> sz;
    vec = vector<int>(sz);
    for (int i = 0; i < sz; i++) {
        cin >> vec[i];
    }
    cout << Solve() << endl;
    return 0;
}

int Solve() {
    int answer = 0;
    if (vec.size() < 3) {
        return answer;
    }
    vector<int> tmp = vec;
    bool smaller_now = true;
    int res1 = 0;
    for (int i = 1; i < vec.size(); i++) {
        if (smaller_now && tmp[i - 1] <= tmp[i]) {
            tmp[i] = INT_MIN;
            res1++;
        } else if (!smaller_now && tmp[i - 1] >= tmp[i]) {
            tmp[i] = INT_MAX;
            res1++;
        }
        smaller_now = !smaller_now;
    }
    tmp = vec;
    smaller_now = false;
    int res2 = 0;
    for (int i = 1; i < vec.size(); i++) {
        if (smaller_now && tmp[i - 1] <= tmp[i]) {
            tmp[i] = INT_MIN;
            res2++;
        } else if (!smaller_now && tmp[i - 1] >= tmp[i]) {
            tmp[i] = INT_MAX;
            res2++;
        }
        smaller_now = !smaller_now;
    }
    return min(res1, res2);
}