input: Write a function to predict the next day's forecast temperature using the exponential smoothing algorithm given the past three day's forecast temperatures. The function should take a list of three integers as input and return a float representing the predicted temperature.
  assert predict_temperature([21, 22, 20])==20.5
  assert predict_temperature([10, 15, 12])==13.0
  assert predict_temperature([30, 28, 29])==28.5
  assert predict_temperature([25, 26, 25])==25.5
  assert predict_temperature([18, 20, 19])==19.5
output: def predict_temperature(temps):
      alpha = 0.5
      return alpha * temps[2] + (1 - alpha) * (alpha * temps[1] + (1 - alpha) * temps[0])