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//
// Jan Zachar 12/12/2022
//
#include <iostream>
using namespace std;



int n, a;
int cntr_a, cntr_b;

int tab[500001]{};

int main() {
    ios_base::sync_with_stdio(0);
    cout.tie(0);
    cin.tie(0);

    cin >> n;

    for (int i = 0; i < n; i++) cin >> tab[i];
    
    for (int i = 1; i < n; i++) {
        if (i%2 && tab[i-1] <= tab[i]) {
            tab[i] = -1000000000;
            ++cntr_a;
        } else if (!(i%2) && tab[i-1] >= tab[i]) {
            tab[i] = 1000000000;
            ++cntr_a;
        }
    }

    for (int i = 1; i < n; i++) {
        if (!(i%2) && tab[i-1] <= tab[i]) {
            tab[i] = -1000000000;
            ++cntr_b;
        } else if (i%2 && tab[i-1] >= tab[i]) {
            tab[i] = 1000000000;
            ++cntr_b;
        }
    }

    cout << min(cntr_a, cntr_b) << endl;
}