print((function (f, _, s)
	return f(s)
end)(function (s)
	local a,r = {},0
	for e in s:gmatch("%d+") do table.insert(a,tonumber(e)) end
	for i=2,#a-1 do if a[i-1]~=a[i+1] and ((a[i]>a[i-1] and a[i]>a[i+1]) or (a[i]<a[i-1] and a[i]<a[i+1])) then r=r+1 end end
	return r
end, io.stdin:read("*l"), io.stdin:read("*l")))