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#include <bits/stdc++.h>

using namespace std;

const int M = 50000 + 100;

int tab[M];

int main() {

    int n, res1 = 0, res2 = 0, prev;
    cin >> n;

    // Start with up:
    for (int i = 0; i < n; ++i) {
        cin >> tab[i];
        if (i % 2) {
            if (prev >= tab[i]) {
                prev = INT_MAX;
                res1++;
            }
            else {
                prev = tab[i];
            }
        }
        else if (i > 0) {
            if (prev <= tab[i]) {
                prev = INT_MIN;
                res1++;
            }
            else {
                prev = tab[i];
            }
        }
        else prev = tab[i];
    }

    // Start with down:
    for (int i = 0; i < n; ++i) {
        if (i % 2) {
            if (prev <= tab[i]) {
                prev = INT_MIN;
                res2++;
            }
            else {
                prev = tab[i];
            }
        }
        else if (i > 0) {
            if (prev >= tab[i]) {
                prev = INT_MAX;
                res2++;
            }
            else {
                prev = tab[i];
            }
        }
        else prev = tab[i];
    }

    cout << min(res1, res2) << "\n";

}

/*
5
4 1 3 3 1
*/