input: Write a function to apply the exponential smoothing algorithm on the past three days' forecast temperatures and predict the next day's forecast temperature. If the provided list of temperatures is fewer than three days, the function should return None.
  assert predict_temperature([21, 22, 20]) == 21.0
  assert predict_temperature([19, 20, 21]) == 20.5
  assert predict_temperature([15, 18, 20]) == 19.0
  assert predict_temperature([25, 24, 23]) == 23.5
  assert predict_temperature([]) == None
  assert predict_temperature([10, 12]) == None
output: def predict_temperature(temps):
      if len(temps) < 3:
          return None
      alpha = 0.5
      smoothed_value = alpha * temps[-1] + (1 - alpha) * (alpha * temps[-2] + (1 - alpha) * temps[-3])
      return smoothed_value