def extract_helm_from_json(input_json):
    """Extracts the HELM strings out of a JSON array.

    :param input_json: JSON array of Peptide objects
    :return: output_helm: string (extracted HELM strings separated by a newline)
    """
    output_helm = ""
    for peptide in input_json:
        if len(output_helm) > 0:
            output_helm += "\n"
        output_helm += peptide["HELM"]
    return output_helm