#include <iostream>

int main(int argc, char *argv)
{
	int n, a, b, c, count = 0;
	std::cin >> n;

	std::cin >> a >> b >> c;

	for (int i = 4; i <= n; ++i)
	{
		if (a < b && b < c)
		{
			count = count + 1;
		}
		a = b;
		b = c;
		std::cin >> c;
	}
	std::cout << count << '\n';
	return 0;
}