#include <iostream>

int main()
{
	int n,b,a,c,count=0;
	std::cin >> n;
	if(n > 2){
		std::cin >> a >> b >> c;
		for(int i = 0; i < n; i++){
			if((a<b)&&(b>c)) count++;
			a = b;
			b = c;
			std::cin >> c;
		}
		std::cout << count;
	}
	else std::cout << "1";
}