def get_census_number(df):
    """
    Transforms the census block number into a different format

    Parameters
    ----------
    df : pandas data frame
        The building benchmarking data for a city

    Returns
    ----------
    df
        The modified data frame
    """

    for i in range(len(df)):
        if len(str(df['CensusBlock'][i])) > 11:
            number = df['CensusBlock'][i]
            df.at[i, 'CensusBlock'] = number[7:]

    return df