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import sys


def delta(x, y):
    if x < y:
        return 1
    elif x == y:
        return 0
    else:
        return -1


n = int(sys.stdin.readline())
a = list(map(int, sys.stdin.readline().split()))
d = list(map(delta, a, a[1:]))
s = [2 * (x % 2) - 1 for x in range(n - 1)]
c = [2 * ((x + 1) % 2) - 1 for x in range(n - 1)]
sd = list(map(lambda x, y: x == y, d, s))
cd = list(map(lambda x, y: x == y, d, c))
cs = 0
i = 0
while i < len(sd)-1:
    if not sd[i]:
        cs += 1
        if not sd[i+1]:
            i += 1
    i += 1
if i < len(sd) and not sd[i]:
    cs += 1
cc = 0
i = 0
while i < len(cd)-1:
    if not cd[i]:
        cc += 1
        if not cd[i+1]:
            i += 1
    i += 1
if i < len(cd) and not cd[i]:
    cc += 1
print(min(cs, cc))