class Stack:
    def __init__(self):
        self._items = []

    def push(self, item):
        self._items.append(item)

    def pop(self):
        if not self.is_empty():
            return self._items.pop()
        raise IndexError("Stack is empty")

    def peek(self):
        if not self.is_empty():
            return self._items[-1]
        raise IndexError("Stack is empty")

    def is_empty(self):
        return len(self._items) == 0

    def size(self):
        return len(self._items)

# Example Usage:
my_stack = Stack()
my_stack.push(10)
my_stack.push(20)
print(f"Stack size: {my_stack.size()}")
print(f"Top element: {my_stack.peek()}")
print(f"Popped: {my_stack.pop()}")
print(f"Stack size after pop: {my_stack.size()}")
print(f"Is stack empty? {my_stack.is_empty()}")