import pandas as pd

def calculate_ema(prices, period=20):
    """
    Calculates the Exponential Moving Average (EMA) for the given period.

    Parameters:
    - prices (pd.Series): A pandas Series containing the stock's closing prices.
    - period (int): The period over which to calculate the EMA. Defaults to 20.

    Returns:
    - pd.Series: A pandas Series containing the EMA values.
    """
    ema = prices.ewm(span=period, adjust=False).mean()
    return ema

if __name__ == "__main__":
    # Example usage
    # Create a sample pandas Series of closing prices
    data = {'Close': [22, 24, 23, 25, 26, 28, 27, 29, 30, 32, 31, 33]}
    prices = pd.Series(data['Close'])
    
    # Calculate the 20-period EMA
    ema20 = calculate_ema(prices, 20)
    print("20-period EMA:")
    print(ema20)
    
    # Calculate the 50-period EMA
    ema50 = calculate_ema(prices, 50)
    print("\n50-period EMA:")
    print(ema50)