from functools import reduce
def f(array):
evenElements = array[::2]
if sorted(evenElements) == evenElements:
return reduce(lambda x, y: x * y, evenElements, 1)
else:
return [i for i, x in enumerate(array) if x > 0]
lst = list(map(int, input().split()))
print(f(lst))
ZnJvbSBmdW5jdG9vbHMgaW1wb3J0IHJlZHVjZQoKZGVmIGYoYXJyYXkpOgoJZXZlbkVsZW1lbnRzID0gYXJyYXlbOjoyXQoJaWYgc29ydGVkKGV2ZW5FbGVtZW50cykgPT0gZXZlbkVsZW1lbnRzOgoJCXJldHVybiByZWR1Y2UobGFtYmRhIHgsIHk6IHggKiB5LCBldmVuRWxlbWVudHMsIDEpCgllbHNlOgoJCXJldHVybiBbaSBmb3IgaSwgeCBpbiBlbnVtZXJhdGUoYXJyYXkpIGlmIHggPiAwXQoKbHN0ID0gbGlzdChtYXAoaW50LCBpbnB1dCgpLnNwbGl0KCkpKQpwcmludChmKGxzdCkp