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#include <iostream>

using namespace std;

const int MAXN = 500 * 100 + 3;

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    
    int n, wynik = 0; cin >> n;
    int wartosci[MAXN], tab[MAXN] = {0};
    
    for (int i = 0; i < n; i++)
        cin >> wartosci[i];
    
    if (wartosci[0] > wartosci[1])
        tab[0] = 2;
    else if ( wartosci[0] < wartosci[1])
        tab[0] = 1;
    
    for (int i = 1; i < n; i++)
    {
        if (wartosci[i] > wartosci[i-1])
            tab[i] = 2;
        else if (wartosci[i] < wartosci[i-1])
            tab[i] = 1;
        else
            tab[i] = 0;
    }
    
    for (int i = 1; i < n; i++)
    {
        if (tab[i] == 0)
        {
                if (tab[i-1] == 1){
                    tab[i] = 2; tab[i+1] = 1;
                    wynik++;
                }
                else if (tab[i-1] == 2){
                    tab[i] = 1; tab[i+1] = 2;
                    wynik++;
                }
                else{
                    if (tab[i+1]==1){
                        tab[i] = 2; wynik++;
                    }
                    else if (tab[i+1]==2){
                        tab[i] = 1; wynik++;
                    }
                    else{
                        tab[i] = 1; wynik++;
                    }
                }
        }
        if (tab[i] == 1)
        {
                if (tab[i-1] == 1){
                    tab[i] = 2;
                    tab[i+1] = 1;
                    wynik++;
                }
        }
        if (tab[i] == 2)
        {
            if (tab[i-1] == 2){
                tab[i] = 1;
                tab[i+1] = 2;
                wynik++;
            }
        }
    }
    
    cout << wynik << '\n';
    
    return 0;
}