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value = int(input())
inp = input().split()
i = 1
answ = 0
sum1 = 0
sum2 = 0
while i < value:
    if inp[i] < inp[i-1]:
        if i%2 == 0:
            sum1 += 1
    else:
        if inp[i] > inp[i-1]:
            if i%2 == 0:
                sum2 += 1
        else:
            sum1 += 1
            sum2 += 1
            i += 1
    i += 1
print(min(sum1, sum2))