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#include <algorithm>
#include <fstream>
#include <string>
#include <sstream>
#include <iostream>
#include <vector>


void tokenize(std::string const& str, const char delim,
	std::vector<std::string>& out)
{
	// construct a stream from the string
	std::stringstream ss(str);

	std::string s;
	while (std::getline(ss, s, delim)) {
		out.push_back(s);
	}
}


int main()
{
	
	std::ifstream file;

	file.open("orn.in");

	if (file.is_open())
	{
		//Get numbers from file
		std::string line;
		std::vector<std::string> string_numbers;

		std::getline(file, line);
		int length = std::stoi(line);

		std::getline(file, line);
		tokenize(line, ' ', string_numbers);

		std::vector<int> numbers;
		for (auto str_num : string_numbers)
		{
			numbers.push_back(std::stoi(str_num));
		}
		
		std::vector<int> numbers1;


		//Do the algorithm 
		int i = 0;
		int changed[6] = { -1, -1, -1, -1, -1, -1 };
		/*int changed5 = -1;
		int changed6 = -1;
		int changed1 = -1;
		int changed2 = -1;
		int changed3 = -1;
		int changed4 = -1;
		*/
		numbers1 = numbers;
		if (numbers1[i + 1] > numbers1[i])
		{
			changed[4] = 0;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = -(2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[4];
				}
			}
		}
		i = 0;
		numbers1 = numbers;
		if (numbers1[i + 1] < numbers1[i])
		{
			changed[5] = 0;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = (2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[5];
				}
			}
		}
		i = 0;
		numbers1 = numbers;
		if (numbers1[i + 1] == numbers1[i])
		{
			changed[0] = 0;
			changed[1] = 0;
			changed[2] = 0;
			changed[3] = 0;
			++changed[0];
			++changed[1];
			++changed[2];
			++changed[3];
			//4 possibilities:

			//first bigger
			i = 0;
			numbers1 = numbers;
			numbers1[i] = 2'147'483'640;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = (2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[0];
				}
			}
			//first smaller
			i = 0;
			numbers1 = numbers;
			numbers1[i] = -2'147'483'640;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = -(2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[1];
				}
			}
			//second bigger
			i = 0;
			numbers1 = numbers;
			numbers1[i + 1] = 2'147'483'640;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = -(2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[2];
				}
			}
			//second smaller
			i = 0;
			numbers1 = numbers;
			numbers1[i + 1] = -2'147'483'640;
			for (int i = 1; i < length - 1; ++i)
			{
				//for even i -1, for uneven i 1
				int sign = (2 * (i % 2) - 1);
				if (sign * numbers1[i + 1] > sign * numbers1[i])
				{
					;//do nothing
				}
				else
				{
					numbers1[i + 1] = -2'147'483'640; //change to smallest possible (with some room)
					++changed[3];
				}
			}
		}
		/*
		std::cout << changed[0] << '\n';
		std::cout << changed[1] << '\n';
		std::cout << changed[2] << '\n';
		std::cout << changed[3] << '\n';
		std::cout << changed[4] << '\n';
		std::cout << changed[5] << '\n';
		*/
		std::vector<int> results;

		for (int n : changed)
		{
			if (n > -1)
			{
				results.push_back(n);
			}
		}

		std::sort(results.begin(), results.end());

		std::cout << results[0];
	}


	file.close();
}