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

int main()
{
    int n;
    cin >> n;

    vector <int> a1(n);
    vector <int> a2(n);

    for(int i = 0; i < n; i++)
    {
        cin >> a1[i];
        a2[i] = a1[i];
    }

    int wyn1 = 0;
    int wyn2 = 0;

    for (int i = 0; i < n - 1; i++)
    {
        if (i % 2 == 0)
        {
            if(a1[i] >= a1[i+1])
            {
                a1[i+1] = 1000000000;
                wyn1++;
            }
        }
        else 
        {
            if(a1[i] <= a1[i+1])
            {
                a1[i+1] = -1000000000;
                wyn1++;
            }
        }
    }

    for (int i = 0; i < n - 1; i++)
    {
        if (i % 2 == 1)
        {
            if(a2[i] >= a2[i+1])
            {
                a2[i+1] = 1000000000;
                wyn2++;
            }
        }
        else 
        {
            if(a2[i] <= a2[i+1])
            {
                a2[i+1] = -1000000000;
                wyn2++;
            }
        }
    }

    cout << min(wyn1, wyn2);
}