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//============================================================================
// Name        : 1b-orn.cpp
// Author      : poz
// Version     :
// Description : https://sio2.mimuw.edu.pl/c/pa-2022-1/p/orn/
//============================================================================

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

int main() {
	const int D = 2'097'152;
	int n;
	cin >> n;
	vector<int> tones_up(n);
	vector<int> tones_down(n);
	for (int i = 0; i < n; i++) {
		cin >> tones_up[i];
		tones_down[i] = tones_up[i];
	}
	int result_up = 0;
	int result_down = 0;
	for (int i = 1; i < n; i++) {
		if (i % 2 == 0) {
			if (tones_up[i - 1] <= tones_up[i]) {
				tones_up[i] -= D;
				result_up++;
			}
			if (tones_down[i - 1] >= tones_down[i]) {
				tones_down[i] += D;
				result_down++;
			}
		} else {
			if (tones_up[i - 1] >= tones_up[i]) {
				tones_up[i] += D;
				result_up++;
			}
			if (tones_down[i - 1] <= tones_down[i]) {
				tones_down[i] -= D;
				result_down++;
			}
		}

	}
	cout << min(result_up, result_down) << endl;
	return 0;
}