def is_json(input_file):
    """
    Check if the file is in JSON format.
    The function reads the first character of the file, and if it is "{" then returns True.

    :param input_file: file name (string)
    :return: Boolean.
    """

    with open(input_file) as unknown_file:
        c = unknown_file.read(1)
        if c == '{':
            return True
        return False