input: def predict_temperature(temperature_list):
      """
      This code uses the exponential smoothing algorithm to predict the next day's forecasted temperature given the past three day's forecasted temperatures.
      >>> predict_temperature([21, 22, 20])
      20.5
      """
output:     alpha = 0.5
      smoothed_value = alpha * temperature_list[-1] + (1 - alpha) * predict_temperature(temperature_list[:-1]) if len(temperature_list) > 1 else temperature_list[0]
      return smoothed_value