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#include<bits/stdc++.h>

using namespace std;

constexpr int inf = 10000001;

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

    int n; cin >> n;
    vector<int> in(n);
    for (int i = 0; i < n; i++)
        cin >> in[i];

    int ans = inf;
    for (int dir : {0, 1}) {
        vector<int> a(in);
        int changes = 0;
        for (int i = 1; i < n; i++) {
            bool should_go_up = bool((i + dir) % 2);
            if (should_go_up and a[i] <= a[i - 1]) {
                a[i] = inf; 
                changes++;
            }
            if (not should_go_up and a[i] >= a[i - 1]) {
                a[i] = -inf;
                changes++;
            }
        } 
        ans = min(ans, changes);
    }
    cout << ans << "\n";
}