4n glasses

There are 4n glasses standing next to each other in a row, the first n of them filled with green tea, the second n of them filled with oolong tea, the third n of them filled with boba tea, and the remaining n glasses are empty. Make the glasses alternate in a green tea - oolong tea - boba tea - empty pattern in the minimum number of glass moves.

The answer I recieved before on this was not right. The professor said it was wrong. Need another answer. Thanks.