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

const int INF = 1e9;

int check(vector<int> tab, int index_to_check) {
    int result = 0;

    for (int i = 1; i < tab.size(); ++i) {
        if (i % 2 == index_to_check) {
            result += !(tab[i - 1] > tab[i]);
            if (!(tab[i - 1] > tab[i])) {
                tab[i] = -INF;
            } 
        } else {
            result += !(tab[i - 1] < tab[i]);
            if (!(tab[i - 1] < tab[i])) {
                tab[i] = INF;
            } 
        }
    }

    return result;
}

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

    int N;
    cin >> N;
    vector<int> tab(N);

    for (auto &p: tab)
    {
        cin >> p;
    }

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


    return 0;
}