def parse_relative_day_value(relative_day: str) -> int:
    """
    Parses a relative day value such as "昨日"
    :param relative_day: The day to parse
    :return: An integer representing the relative value of the day, for example -1
    """
    if relative_day == "前月":
        return -1
    if relative_day == "今月":
        return 0
    if relative_day == "来月":
        return 1
    raise ValueError(f"Could not parse the input as a relative month: {relative_day}")