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#include <bits/stdc++.h>

int main() {
    std::ios_base::sync_with_stdio(0); std::cin.tie(NULL);
    int n;
    std::cin >> n;
    std::vector<int> w(n, 0);
    for (auto &x : w) std::cin >> x;
    const int MAX = 1e9;

    // a_0 < a_1
    int res1 = 0;
    std::vector<int> v = w;
    for (int i = 0; i < n-1; i++) {
        if (i % 2 == 0 && v[i] >= v[i+1]) {
            res1++; v[i+1] = MAX;
        } else if (i % 2 == 1 && v[i] <= v[i+1]) {
            res1++; v[i+1] = -MAX;
        }
    }

    // a_0 > a_1
    int res2 = 0;
    v = w;
    for (int i = 0; i < n-1; i++) {
        if (i % 2 == 0 && v[i] <= v[i+1]) {
            res2++; v[i+1] = -MAX;
        } else if (i % 2 == 1 && v[i] >= v[i+1]) {
            res2++; v[i+1] = MAX;
        }
    }

    std::cout << std::min(res1, res2) << "\n";
}