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#include <cstdio>
#include <cstdlib>
#include <iostream>

using namespace std;

#define NMAX 50001
int t[NMAX];

int main() {
        int n;

        cin >> n;
        for(int i =0 ;i < n;i++)
                cin >> t[i];

        int best = NMAX;
        int cnt = 0;

        for (int i = 1; i < n; i++) {
                if (i % 2 == 0) {
                        if (t[i] < t[i-1]) {
                                continue;
                        } else {
                                cnt++;
                                i++;
                                continue;
                        }
                } else {
                        if (t[i] > t[i-1]) {
                                continue;
                        } else {
                                cnt++;
                                i++;
                                continue;
                        }
                }
        }
        if (cnt < best)
                best = cnt;

        cnt = 0;
        for (int i = 1; i < n; i++) {
                if (i % 2 == 0) {
                        if (t[i] > t[i-1]) {
                                continue;
                        } else {
                                cnt++;
                                i++;
                                continue;
                        }
                } else {
                        if (t[i] < t[i-1]) {
                                continue;
                        } else {
                                cnt++;
                                i++;
                                continue;
                        }
                }
        }
        if (cnt < best)
                best = cnt;

        cout << best << endl;


        return 0;
}