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#include <bits/stdc++.h>
using namespace std;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int n;
	cin >> n;
	vector <int> v(n), d(n-1);
	for (int i = 0; i < n; i++) {
		cin >> v[i];
	}
	for (int i = 0; i < n-1; i++) {
		if (v[i+1] - v[i] > 0)
			d[i] = 1;
		else if (v[i+1] - v[i] < 0)
			d[i] = -1;
		else
			d[i] = 0;
	}
	auto c = d;
	int wyn = 0;
	for (int i = 0; i < n-1; i++) {
		if (i % 2 && c[i] != -1) {
			c[i] = -1;
			if (i != n-2) c[i+1] = 1;
			wyn++;
		}
		else if (!(i % 2) && c[i] != 1) {
			c[i] = 1;
			if (i != n-2) c[i+1] = -1;
			wyn++;
		}
	}
	int res = wyn;
	wyn = 0;
	for (int i = 0; i < n-1; i++) {
		if (i % 2 && d[i] != 1) {
			d[i] = 1;
			if (i != n-2) d[i+1] = -1;
			wyn++;
		}
		else if (!(i % 2) && d[i] != -1) {
			d[i] = -1;
			if (i != n-2) d[i+1] = 1;
			wyn++;
		}
	}
	res = min(res, wyn);
	cout << res << "\n";

}