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#include <iostream>
#include <vector>

using namespace std;

int main()
{
	const int MAX_LEN = 50001;
	int n, val;
	cin >> n;
	vector <int> v;
	bool odds[MAX_LEN];
	bool evens[MAX_LEN];

	for (int i = 0; i < n; i++) {
		cin >> val;
		v.push_back(val);
	}

	for (int i = 0; i < n; i++) {
		bool before = (i == 0) || (v[i] > v[i - 1]);
		bool after = (i == n - 1) || (v[i] > v[i + 1]);
		bool* s;

		if (i % 2 == 0) {
			s = evens;
		}
		else {
			s = odds;
		}

		if (!before && !after && !s[i-1]) {
			s[i] = 1;
		}
		else {
			if (!before) {
				s[i - 1] = 1;
			}

			if (!after) {
				s[i + 1] = 1;
			}
		}
	}

	int result = 0;
	int even_res = 0;
	int odd_res = 0;

	for(int i = 0; i < n; i++) {
        even_res += evens[i];
        odd_res += odds[i];
	}

	if (even_res < odd_res) {
		result = even_res;
	}
	else {
		result = odd_res;
	}

	cout << result << '\n';
}