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#include <cstdio>
#include <vector>
using namespace std;
constexpr int INF = 1e9;

int n;
vector<int> a, b;

int solve(vector<int> &arr, int rem) {
	int cnt = 0;
	for (int i = 1; i < n; ++i) {
		if (i%2 == rem && arr[i-1] >= arr[i]) {
			arr[i] = INF;
			++cnt;
		}
		if (i%2 != rem && arr[i-1] <= arr[i]) {
			arr[i] = -INF;
			++cnt;
		}
	}

	return cnt;
}

int main(void) {
	scanf("%d", &n);
	a.resize(n);
	b.resize(n);
	for (int i = 0; i < n; ++i) {
		scanf("%d", &a[i]);
		b[i] = a[i];
	}

	int result = min(
			solve(a, 0),
			solve(b, 1));
	printf("%d\n", result);

	return 0;
}