#coding: UTF-8

import sys
import re
import itertools
from math import log
from collections import deque

### defs ###
def monmatsu(A):
	mn = min(A)
	mx = max(A)
	if (A[0]==A[1] or A[0]==A[2] or A[1]==A[2]):
		return False
	if (A[1]!=mn and A[1]!=mx):
		return False
	else:
		return True

### main ###
N = int(sys.stdin.readline())
A = list(map(int, sys.stdin.readline().split()))

ans=0
for i in range(N-2):
	if (monmatsu(A[i:i+3])):
		ans+=1
print(ans)