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#include <bits/stdc++.h>

using namespace std;

#ifdef D
#define DEBUG(x)        \
    do {                \
        x               \
        cout.flush();   \
    } while (0)
#else
#define DEBUG(x)
#endif

using ll = long long;

const int NMAX = 5e4 + 7, D = 1e6 + 7;

int n, ra, rb;
int t[NMAX], a[NMAX];

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> n;

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

    for (int i = 1; i < n; ++i) {
        if (i % 2) {
            if (t[i] <= t[i - 1]) {
                t[i] = D;
                ra++;
            }
        } else {
            if (t[i] >= t[i - 1]) {
                t[i] = -D;
                ra++;
            }
        }
    }

    for (int i = 1; i < n; ++i) {
        if (i % 2) {
            if (a[i] >= a[i - 1]) {
                a[i] = -D;
                rb++;
            }
        } else {
            if (a[i] <= a[i - 1]) {
                a[i] = D;
                rb++;
            }
        }
    }

    cout << min(ra, rb);

    return 0;
}