import pandas as pd

def calculate_ema(prices, periods):
    """
    Calculates the Exponential Moving Averages (EMA) for the given periods.
    
    Parameters:
    - prices (pd.Series): A pandas Series containing the stock's closing prices.
    - periods (list of int): A list of integers representing the periods over which to calculate the EMAs.
    
    Returns:
    - dict of pd.Series: A dictionary where each key is the period, and the value is a pandas Series containing the EMA values for that period.
    """
    emas = {}
    for period in periods:
        ema = prices.ewm(span=period, adjust=False).mean()
        emas[period] = ema
    return emas

if __name__ == "__main__":
    # Example usage
    data = {'Close': [22, 24, 23, 25, 26, 28, 27, 29, 30, 32, 31, 33]}
    prices = pd.Series(data['Close'])
    
    # User-defined EMA periods
    periods = [20, 50]  # Example: 20-day and 50-day EMAs
    
    # Calculate EMAs for specified periods
    ema_values = calculate_ema(prices, periods)
    
    for period, ema in ema_values.items():
        print(f"{period}-period EMA:")
        print(ema)
        print()