def get_top(df, quantile):
    """
    This function returns the top X% of runners based on finish time.
    :param dataframe df: a dataframe containing marathon split times for individuals
    :param float quantile: a decimal specifying the desired cutoff for performance
    :return dataframe subset_winners: dataframe containing times for top individuals
    """
    quantile_value = df["overall"].quantile(quantile)
    subset_winners = df.loc[(df["overall"] <= quantile_value)].copy()
    return subset_winners