Suppose you are given a stack of n pancakes of different sizes. You want to

sort the pancakes so that smaller pancakes are on top of larger pancakes.

The only operation you can perform is a flip$$insert a spatula under the

top k pancakes, for some integer k between $1$ and n$,$ and flip them all over.

For every positive integer n$,$ describe a stack of n pancakes that requires

$($n$)$ flips to sort.