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#include <bits/stdc++.h>


int brutal_force(std::vector<int> v, int n, bool start)
{
	// std::cerr << "run with up = " << start << "\n";
	int prev = v[0];

	bool up = start;
	int sum = 0;
	for(int i=1;i<n;i++)
	{
		int& cur = v[i];
		// std::cerr << "i = " << i << "\tcur=" << cur << "\tprev = " << prev << "\t" << (up ? "UP" : "DOWN") << "\t";
		int next = 0;
		if(i+1 != 0)
		{
			next = v[i+1];
			// std::cerr << "next = " << next << "\t";
		}
		if(up && cur <= prev)
		{
			// std::cerr << "UP & LE";
			sum++;
			if(i+1 != 0)
			{
				int max = std::max(prev, next);
				cur = max+1;
			}
			else cur = 1000001;
			// std::cerr << "\tcur = " << cur << "\t";
		}
		else if(!up && cur >= prev)
		{
			// std::cerr << "!UP & GE";

			sum++;
			if(i+1 != 0)
			{
				int min = std::min(prev, next);
				cur = min-1;
			}
			else cur = -1000001;
			// std::cerr << "\tcur = " << cur << "\t";
		}

		// std::cerr << "\n";
		
		prev = cur;

		up = !up;
	}

	// std::cerr << "sum = " << sum << "\n===\n";

	return sum;
}


int main()
{
	std::ios_base::sync_with_stdio(0);
	
	int n;
	std::cin >> n;
	std::vector<int> v(n);
	for(int i=0;i<n;i++)
	{
		std::cin >> v[i];
	}

	int a = brutal_force(v, n, true);
	int b = brutal_force(v, n, false);
	int sum = std::min(a, b);
	
	std::cout << sum << "\n";

	return 0;
}