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#include <bits/stdc++.h>
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define per(i, a, b) for (int i = b; i >= a; i--)
#define cat(x) cout << #x << ": " << x << endl

using namespace std;
using ll = long long;

const int N = 50500;
int n, a[N];

int main() {
	cin.tie(0)->sync_with_stdio(0);

	cin >> n;
	rep(i, 1, n) cin >> a[i];

	int res = n;
	rep(f, 0, 1) {
		int cur = 0;
		int cnt = 1;
		rep(i, 2, n) {
			if (a[i - 1] == a[i] || (f ^ (i % 2)) != (a[i - 1] < a[i])) {
				cnt++;
			} else {
				cur += cnt / 2;
				cnt = 1;
			}
		}
		cur += cnt / 2;
		res = min(res, cur);
	}
	cout << res << "\n";

	return 0;
}