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#include <iostream>
#include <algorithm>

using namespace std;

int n, A[1000000], cop[1000000], ans1 = 0, ans2 = 0;
bool b;

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

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

    copy(begin(A), end(A), begin(cop));
    b = false;
    for (int i = 0; i < n - 1; i++)
    {
        if (b && cop[i + 1] <= cop[i]) {
            ans1++;
            cop[i+1] = 1000000;
        }
        else if (!b && cop[i + 1] >= cop[i]) {
            ans1++;
            cop[i+1] = -1000000;
        }
        b = !b;
    }

    b = true;
    for (int i = 0; i < n - 1; i++)
    {
        if (b && A[i + 1] <= A[i]) {
            ans2++;
            A[i+1] = 1000000;
        }
        else if (!b && A[i + 1] >= A[i]) {
            ans2++;
            A[i+1] = -1000000;
        }
        b = !b;
    }

    cout << min(ans1,ans2);
}