input: def predict_temperature(temperature_list: List[int]) -> float:
      """ 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 = temperature_list[-1]
      for i in range(2, -1, -1):
          smoothed_value = alpha * temperature_list[i] + (1 - alpha) * smoothed_value
      return smoothed_value