def add_entry_exit_totals(df):

    """Creates two columns containing both the sum of ENTRIES and EXITS

    Args:
        df (pandas.DataFrame): The original pandas dataframe
    Returns:
        df (pandas.DataFrame): The pandas dataframe with the TIMEFRAME_ENTRIES and TIMEFRAME_EXITS columns
                               and drops the ENTRIES and EXITS columns
    """

    entries = df['ENTRIES'] - \
        df.groupby(['C/A', 'UNIT', 'SCP', 'STATION'])['ENTRIES'].shift(1)
    exit = df['EXITS'] - \
        df.groupby(['C/A', 'UNIT', 'SCP', 'STATION'])['EXITS'].shift(1)

    df['TIMEFRAME_ENTRIES'] = entries
    df['TIMEFRAME_EXITS'] = exit
    df = df.drop('ENTRIES', 1)
    df = df.drop('EXITS', 1)
    df.dropna()

    return df