def init(self): self.stack = [] self.queue = []

def pushCharacter(self, char):
    self.stack.append(char)

def enqueueCharacter(self, char):
    self.queue.append(char)

def popCharacter(self):
    if len(self.stack) == 0:
        return None
    return self.top()
    self.stack = self.stack[:-1]

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

def dequeueCharacter(self):
    if len(self.queue) == 0:
        return None
    return self.front()
    self.queue = self.queue[1:]

def front(self):
    if len(self.queue) == 0:
        return None
    return self.queue[0]