class MinStack:

    def __init__(self):
        self.stack = []
        self.minEl = None

    def push(self, x: int) -> None:
        node = Node(x)
        if self.minEl is None or node.value <= self.minEl.value:
            node.lastMin = self.minEl
            self.minEl = node
        self.stack.append(node)

    def pop(self) -> None:
        if len(self.stack) > 0:
            ret = self.stack[len(self.stack) - 1]
            if ret.value == self.minEl.value:
                self.minEl = self.minEl.lastMin
            self.stack = self.stack[0:len(self.stack) - 1]
            return ret.value
        return None

    def top(self) -> int:
        if len(self.stack) > 0:
            return self.stack[len(self.stack) - 1].value
        return None

    def getMin(self) -> int:
        return self.minEl.value

    def __str__(self):
        str_result = ""
        for x in self.stack:
            str_result += "\n"
            str_result += str(x)
        return str_result
    
class Node:
    def __init__(self, x, lastMin = None):
        self.value = x
        self.lastMin = lastMin
        
    def __str__(self):
        return f"Value: {str(self.value)} Last Min: {str(self.lastMin)}"

# Your MinStack object will be instantiated and called as such:
values = []
obj = MinStack()
obj.push(-2)
obj.push(0)
obj.push(-3)
values.append(obj.getMin())
values.append(obj.pop())
values.append(obj.top())
values.append(obj.getMin())

print("Expected: [-3, -3, 0, -2]")
print("Got:", values)