def remove_nan(df):
    """Remove ``NaN`` and reindex.
    
    Args:
        df (pd.DataFrame): Dataframe.
    
    Returns:
        pd.DataFrame: Dataframe without NaN.
    
    Examples:
        >>> df = pd.DataFrame({'letters':['a','a','c'], 'numbers':[1,None,3]})
        >>> df_return = remove_nan(df)
        >>> df_return
          letters  numbers
        0       a      1.0
        1       c      3.0
    """
    return df.dropna().reset_index(drop=True)