Minimum Stack

Design a stack that supports the following operations: push, pop, top, and retrieving the minimum element in constant time. Your implementation should be a class `MinStack` with methods: `push(val: int), pop(), top() -> int, get_min() -> int`. ### Input A sequence of operations mixed with integers, such as 'push 1', 'pop', 'get_min', etc. ### Output After all operations, print the minimum element in the stack. If the stack is empty when 'get_min' is called, return 'None'. ### Example Input: push 5 push 3 push 8 get_min pop get_min Output: 3 5