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#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int n;
    cin >> n;
    vector<int> sounds(n);
    for (auto& i : sounds)
        cin >> i;

    auto check = [&](int order) {
        vector<int> local_sounds = sounds;
        int ans = 0;
        for (int i = 1; i < n; i++) {
            if (i % 2 == order) {
                if (local_sounds[i] >= local_sounds[i - 1])
                    ans++, local_sounds[i] = INT_MIN;
            } else {
                if (local_sounds[i] <= local_sounds[i - 1])
                    ans++, local_sounds[i] = INT_MAX;
            }
        }
        return ans;
    };

    cout << min(check(0), check(1)) << "\n";

    return 0;
}