def pop(self):
if deque.size() == 0:
return -1
else:
return self.deque.popleft()
def back(self):
if deque.size() == 0:
return -1
else:
return self.deque[-1]
def empty(self):
if deque.size() == 0:
return 1
else:
return 0
def front(self):
if deque.size() == 0:
return -1
else:
return self.deque[0]
def front(self):
if deque.size() == 0:
return -1
else:
return self.deque[0]
def back(self):
if deque.size() == 0:
return -1
else:
return self.deque[-1]
deque = Queue()
N = int(sys.stdin.readline())
for i in range(N):
str = sys.stdin.readline().rstrip().split(' ')
if str[0] == 'push':
deque.push(int(str[1]))
elif str[0] == 'front':
print(deque.front())
elif str[0] == 'size':
print(deque.size())
elif str[0] == 'empty':
print(deque.empty())
elif str[0] == 'back':
print(deque.back())
elif str[0] == 'pop':
print(deque.pop())