1 barrel is the third time that Li Bai drank wine, and the third time he added double wine in the restaurant. Since it is the last time to drink, it can be considered that before adding wine, 1 divided by 2 is equal to 0.5 barrels. Before the third drink, it was 0.5, so before the second drink, it was 1.5, and the wine doubled again, indicating that there was 0.75 left after the first drink.

From the second time to the first time, I met a shop to drink. The drinking rate was 0.75, and before drinking, it was 1.75. Before I met the store for the first time, it was 1.75 divided by 2 equals 0.875, which is the original wine in the pot.