Random left motion from right to left of movie clip in the striaght motion

1

I want to ask about do anyone know how to set the movie clip move from right to left with random height move out from the stage? The movie clip need to set on the certain part of the stage.For example: a person is walking on the road from right to left, but he comes out from different height of the right boundary of the stage.Do anyone know how to set? I have thought about it in the whole day time.I have attached my flash game file.Thank you.