Martial arts cheats python implementation

problem

小明到X山洞探险，捡到一本有破损的武功秘籍（2000多页！当然是伪造的）。
他注意到：书的第10页和第11页在同一张纸上，但第11页和第12页不在同一张纸上。
小明只想练习该书的第81页到第92页的武功，又不想带着整本书。请问他至少要撕下多少张纸带走？

Idea and code

Idea:
According to page 10-11, even number starts with odd number ends with one page.
So 80 and 81 are pages, 92-93 are pages,
so 82-91 are 5 pages.
So solve the case: 7 pages. I
don’t even want to write code.

def solve(m, n):
    num = 0
    if m % 2 == 0:
        if n % 2 == 0:
            num = (n - m) / 2 + 1
        else:
            num = (n - m + 1) / 2 + 1
    elif m % 2 != 0:
        if n % 2 == 0:
            num = (n - m + 1) / 2 + 1
        else:
            num = (n - m) / 2 + 1
    return num


print(solve(81, 92))