def divide_to_groups(calendar):
    # base-case
    if len(calendar) == 0:
        return 0

    arr = []

    # "a" and "b" are used for sorted,
    # they mark the start and the end
    # of a particular array
    for i in calendar:
        arr.append((i[0], "a"))
        arr.append((i[1], "b"))
    arr = sorted(arr)

    grps = 0
    max_grps = 0

    for i in arr:
        if i[1] == "a":
            grps += 1
            if max_grps < grps:
                max_grps = grps
        else:
            grps -= 1

    return max_grps


# Neboj se pridat si vlastni testy
def test_default():
    calendars = [
        [ ],
        [ (1, 2), (3, 3), (500, 800), (50, 56) ],
        [ (1, 2), (5, 8), (1, 3), (1, 1), (3, 6), ]
    ]

    answers = [ 0, 1, 3 ]

    for i in range(len(calendars)):
        result = divide_to_groups(calendars[i])
        if result == answers[i]:
            print("[", i, "] OK.", sep="")
        else:
            print("[", i, "] Not OK. Expected ", answers[i], " but got ", result, ".", sep="")


if __name__ == '__main__':
    test_default()