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n = int(input())
napis = input().split()
rosnie = False
wynik1 = 0
wynik2 = 0

i = 0
while i < n-1:
    if (int(napis[i]) <= int(napis[i+1]) and rosnie == False) or (int(napis[i]) >= int(napis[i+1]) and rosnie == True):
        wynik1 += 1
        i += 1
        rosnie = not rosnie
    rosnie = not rosnie
    i += 1

rosnie = True
j = 0
while j < n-1:
    if (int(napis[j]) <= int(napis[j+1]) and rosnie == False) or (int(napis[j]) >= int(napis[j+1]) and rosnie == True):
        wynik2 += 1
        j += 1
        rosnie = not rosnie
    rosnie = not rosnie
    j += 1

print(min(wynik1, wynik2))