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n = int(input())
a = [int(x) for x in input().split()]
b = [x for x in a]
ra, rb = 0, 0
m = 1000000000
for i in range(n-1):
    if (i % 2):
        if a[i+1] <= a[i]:
            ra += 1
            a[i+1] = m
        if b[i+1] >= b[i]:
            rb += 1
            b[i+1] = -m
    else:        
        if b[i+1] <= b[i]:
            rb += 1
            b[i+1] = m
        if a[i+1] >= a[i]:
            ra += 1
            a[i+1] = -m
print(min(ra, rb))