def get_task_Id(file):
    """ Returns the task_id for structure. It's an id which uniquely
        defines the material for material. It's also known as Material Id
        in the properties files after MD simulation.

        Parameters:
        file (str): file is a string over the path to a file.

        Returns:
        str: returns id number as a string.
    """
    file = open(file, "r")
    lines = file.read().splitlines()
    file.close()
    Id = lines[0].split(":")[1]
    return Id