def ex3_pickle_name(n):
    
    
    """build name for pickle file
    
    Parameters
    ------
    n, prop : float
        `n` population and `proportion` observed
        
    Returns
    ------
    
    f_name : str
        return `f_name` file name to save pickle as
    """
    
    f_name = f"ueg_ukf_agents_{n}.pkl"
    return f_name