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#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main()
{

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int n;
    cin >> n;

    int option1 = 0;
    int option2 = 0;

    vector <int> tab;
    vector <int> tab2;
    tab.resize(n + 5);
    tab2.resize(n + 5);
    for (int i = 0; i < n; i++)
    {
        cin >> tab[i];
        tab2[i] = tab[i];
    }

    for (int i = 1; i < n; i++)
    {
        if (i % 2 == 0)
        {
            if (tab[i] <= tab[i - 1])
            {
                option1++;
                tab[i] = 1000005;
            }
        }
        else
        {
            if (tab[i] >= tab[i - 1])
            {
                option1++;
                tab[i] = -1000005;
            }
        }
    }

    for (int i = 1; i < n; i++)
    {
        if (i % 2 == 1)
        {
            if (tab2[i] <= tab2[i - 1])
            {
                option2++;
                tab2[i] = 1000005;
            }
        }
        else
        {
            if (tab2[i] >= tab2[i - 1])
            {
                option2++;
                tab2[i] = -1000005;
            }
        }
    }

    cout << min(option1, option2);
}