from collections import deque
import sys
input=sys.stdin.readline
num=int(input())
dq=deque()
def empty():
if len(dq)!=0:
return 0
else:
return 1
def size():
return len(dq)
def front():
if len(dq)!=0:
print(dq[0])
else:
print(-1)
def back():
if len(dq)!=0:
print(dq[-1])
else:
print(-1)
for i in range(num):
command=input().split()
if command[0]=='push_front':
dq.appendleft(command[1])
elif command[0]=='push_back':
dq.append(command[1])
elif command[0]=='pop_front':
if len(dq)!=0:
print(dq[0])
dq.popleft()
else:
print(-1)
elif command[0]=='pop_back':
if len(dq)!=0:
print(dq[-1])
dq.pop()
else:
print(-1)
elif command[0]=='size':
print(size())
elif command[0]=='empty':
print(empty())
elif command[0]=='front':
front()
elif command[0]=='back':
back()
접근 방법