i have two stack S1 and S2 the total amount of objects in them is "n" (there is also stack S3 ) in both stack all the objects are sorted in accending order

(the biggest number is on top the smallest number is on the bottom)

and thats the way it goes in both stacks

the question asks me to build a method which puts all of the objects from stacks S1 and S2 into stack S3 in accended order plus we have to accomplish this using 4n-4 moves ?? (the biggest number is on top the smallest number is on the bottom)

i tried to solve that by flipping the stacks using the S3 so they will be sorted from the smallest to the biggest taking two templorary variables pop each object from each stack into the temporary variable and then we compare them and the smallest goes to S3 and the other one waits till we have an object from the other stack which is smaller than him, and then we have to flip S3 in order have the biggest on top also i tried using TOP commang but i found out that its implementation also has push and pop in it. but in that way we have more than 4n-4 moves