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#include <iostream>

using namespace std;

int tab[50001];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n, a, suma = 0;
    cin >> n;
    for (int i = 0; i < n; i++)cin >> tab[i];
    for (int i = 0; i < n - 1; i++) {
        if (i == 0) {
            if (tab[i] > tab[i + 1])a = 0;
            else if (tab[i] < tab[i + 1])a = 1;
            else {
                tab[i + 1] = tab[i + 2] - 1;
                a = 0;
                suma++;
            }
        }
        else if (a % 2 == 1) {
            if (tab[i] <= tab[i + 1]) {
                tab[i + 1] = tab[i + 2] - 1;
                suma++;
                a++;
            }
        }
        else if (a % 2 == 0) {
            if (tab[i] >= tab[i + 1]) {
                tab[i + 1] = tab[i + 2] + 1;
                suma++;
                a++;
            }
        }
    }
    cout << suma;
    /*
    for (int i = 0; i < n; i++)cout << tab[i] << " ";
        cout << endl;
        cout << suma;
        cout << endl;
    */

    return 0;
}