class Stack(object):

def __init__(self,size):

self.index = -1

self.stack = [None] * size

def push(self, value):

if self.index != len(self.stack) -1:

self.index = self.index + 1

self.stack[self.index] = value

def pop(self):

if not self.empty():

value = self.stack[self.index]

self.stack[self.index] = None

self.index = self.index - 1

return value

def peek(self):

if not self.empty():

return self.stack[self.index]

def empty(self):

return self.index == -1