[백준] 10845번 : 큐 with python3

import sys
input = lambda : sys.stdin.readline().strip()

class Queue(object):
    def __init__(self):
        self.dts = []
        self.lvl = 0

    def push(self, x):
        self.dts = [x] + self.dts
        self.lvl += 1

    def pop(self):
        if self.lvl == 0: return -1
        tmp = self.dts[-1]
        self.dts = self.dts[:-1]
        self.lvl -= 1
        return tmp

    def size(self):
        return self.lvl

    def empty(self):
        return 0 if self.dts else 1

    def front(self):
        if self.lvl == 0: return -1
        return self.dts[-1]
        
    def back(self):
        if self.lvl == 0: return -1
        return self.dts[0]

queue = Queue()
for _ in range(int(input())):
    order = input().split()
    if order[0] == 'push':
        queue.push(order[1])
    elif order[0] == 'pop':
        print(queue.pop())
    elif order[0] == 'size':
        print(queue.size())

    elif order[0] == 'empty':
        print(queue.empty())

    elif order[0] == 'front':
        print(queue.front())

    elif order[0] == 'back':
        print(queue.back())