class Problem0116:
	def solve(this):
		n = int(input())
		a = list(map(int, input().split()))
		
		res = 0
		for i in range(len(a) - 2):
			c = a[i:i+3]
			if len(c) != len(set(c)):
				continue
			
			if c[0] < c[1] and c[2] < c[1] or c[1] < c[0] and c[1] < c[2]:
				res += 1
		print(res)

if __name__ == "__main__":
	problem = Problem0116()
	problem.solve()