input: from typing import List
  
  def predict_temperature(temperature_list: List[float]) -> float:
      """
      Predict the next day's forecasted temperature using exponential smoothing algorithm
      given the past three days' forecasted temperatures.
      >>> predict_temperature([21, 22, 20])
      20.5
      >>> predict_temperature([20, 21, 22])
      21.0
      """
      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