class Node:
    def __init__(self):
        self.data = None
        self.nextNode = None

class LLStack:
    def __init__(self):
        self.head = None
        self.tail = None

    def Push(self, value):
        current = Node()
        current.data = value
        if self.head == None:
            current.nextNode = None
            self.head = current
        else:
            current.nextNode = self.head
            self.head = current


    def Pop(self):
        if self.head == None:
            print("Stack Underflow")
        elif self.head.nextNode == None:
            self.head = None
        else:
            self.head = self.head.nextNode

    def viewStack(self):
        outString = ""
        if not(self.head == None):
            current = self.head
            while not(current == None):
                outString = outString + str(current.data) + ", "
                current = current.nextNode
            print(outString)
        else:
            print("Nothing in stack")

stack = LLStack()
stack.viewStack()
stack.Pop()
stack.viewStack()
stack.Push(5)
stack.viewStack()
stack.Push(10)
stack.viewStack()
stack.Pop()
stack.viewStack()
stack.Pop()
stack.viewStack()