GATE CSE 2023 Q59: Top of stack after mixed stack and queue operations

Consider a sequence $a$ of elements $a_0 = 1$, $a_1 = 5$, $a_2 = 7$, $a_3 = 8$, $a_4 = 9$, and $a_5 = 2$. The following operations are performed on a stack $S$ and a queue $Q$, both of which are initially empty.

I: push the elements of $a$ from $a_0$ to $a_5$ in that order into $S$.

II: enqueue the elements of $a$ from $a_0$ to $a_5$ in that order into $Q$.

III: pop an element from $S$.

IV: dequeue an element from $Q$.

V: pop an element from $S$.

VI: dequeue an element from $Q$.

VII: dequeue an element from $Q$ and push the same element into $S$.

VIII: Repeat operation VII three times.

IX: pop an element from $S$.

X: pop an element from $S$.

The top element of $S$ after executing the above operations is _______.