Efficient Min-Tracking List

This problem requires you to implement a custom list data structure that supports the following operations efficiently:

• push x: Append the integer x to the end of the list.
• pop: Remove the last element from the list.
• top: Retrieve the last element in the list without removing it.
• get_min: Retrieve the minimum element in the list in constant time.

Your task is to process a series of commands. For each command that produces an output (top and get_min), you should print the result on a new line. If an operation is invalid (for example, calling top or get_min on an empty list, or pop on an empty list), output error.

Note that the get_min operation must run in constant time, i.e. in \(O(1)\) time.

inputFormat

The first line of input contains a single integer \(n\) representing the number of commands. The following \(n\) lines each contain a command. The commands can be:

• push x where x is an integer.
• pop
• top
• get_min

outputFormat

For each command that produces an output (top or get_min), print the result on its own line. If a command cannot be executed because the list is empty, output error.

## sample

6
push 5
push 3
top
get_min
pop
get_min

3
3
5

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