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#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios_base::sync_with_stdio(0);

    cin.tie(0);
    cout.tie(0);

    int n;
    cin >> n;

    vector<int> voice;

    for (int i = 0; i < n; i++)
    {
        int a;
        cin >> a;
        voice.push_back(a);
    }

    int i = 0, j = 1, k = 2;

    int res = 0;

    while (k < n)
    {

        if (voice[i] < voice[j] && voice[j] > voice[k])
        {
            i++;
            j++;
            k++;
            continue;
        }
        if (voice[i] > voice[j] && voice[j] < voice[k])
        {
            i++;
            j++;
            k++;
            continue;
        }
        res++;

        if (voice[i] < voice[j] || voice[j] > voice[k])
        {
            voice[k] = 1000000;
        }
        if (voice[i] > voice[j] || voice[j] < voice[k])
        {
            voice[k] = -1000000;
        }

        i++;
        j++;
        k++;
    }
    cout << res;
}