栅栏密码Rail Fence Cipher

def solve(____):
    fence = [[] for _ in range(____)]
    rail = ____
    direction = ____
    for c in text:
        fence[rail].append(____)
        rail += direction
        if rail == ____ or rail == rails - ____:
            direction = -direction
    print('____'.join('____'.join(____) for row in fence))