input: 
  from typing import List
  
  
  def predict_temperature(temperature_list: List[float]) -> float:
      """
      Predict the next day's forecasted temperature using the exponential smoothing algorithm based on the past three day's forecasted temperatures.
      >>> predict_temperature([21, 22, 20])
      20.5
      """
      alpha = 0.5  # Confidence value
      predicted_temperature = temperature_list[-1]  # Initializing prediction
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha * temperature + (1 - alpha) * predicted_temperature
      return predicted_temperature
  
output:     alpha = 0.5  # Confidence value
      predicted_temperature = temperature_list[-1]  # Initializing prediction
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha * temperature + (1 - alpha) * predicted_temperature
      return predicted_temperature