What is the sentence before the red flag slowly rolls up to the west wind in ancient poetry?

The red flag is rolled up before the west wind-the peak on Liupan Mountain. This poem comes from the lyrics written by Mao Zedong at 1935- Qingpingle Liupanshan.

Original: the sky is high and the clouds are light, looking at the south geese flying. If you don't reach the Great Wall, you are not a hero, but you will fight for 20,000. At the top of Liupan Mountain, the red flag flutters in the west wind. Holding a long tassel today, when will it be a black dragon?