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#include <bits/stdc++.h>

int n;
int tab[1'000'000];
int tabA[1'000'000];
int tabB[1'000'000];
constexpr int MIN = -1'000'000'000;
constexpr int MAX = 1'000'000'000;

int A(int arr[])
{
    int output = 0;
    for (int i = 1; i < n; ++i)
    {
        if (i % 2) {
            if (arr[i] >= arr[i - 1]) {
                output += 1;
                arr[i] = MIN;
            }
        }
        else {
            if (arr[i] <= arr[i - 1]) {
                output += 1;
                arr[i] = MAX;
            }
        }
    }
    return output;
}

int B(int arr[])
{
    int output = 0;
    for (int i = 1; i < n; ++i)
    {
        if (i % 2){
            if (arr[i] <= arr[i - 1]){
                output += 1;
                arr[i] = MAX;
            }
        }
        else
            if (arr[i] >= arr[i - 1]){
                output += 1;
                arr[i] = MIN;
            }
    }
    return output;
}

int main()
{
    std::cin >> n;
    for (int i = 0; i < n; ++i)
        std::cin >> tab[i];

    std::copy(tab, tab + n, tabA);
    std::copy(tab, tab + n, tabB);

    if (n == 1)
        std::cout << 0;
    else
        std::cout << std::min(A(tabA), B(tabB));
    return 0;
}