class Deque:
left = []
right = []
def push_front(self, x):
self.left.append(x)
def push_back(self, x):
self.right.append(x)
def pop_front(self, x):
if not self.left :
if not self.right:
val = -1
else:
while self.right :
self.left.append(self.right.pop())
val = self.left.pop()
while self.left:
self.right.append(self.left.pop())
else:
val = self.left.pop()
print(val)
def pop_back(self, x):
if not self.right:
if not self.left:
val = -1
else:
while self.left :
self.right.append(self.left.pop())
val = self.right.pop()
while self.right:
self.left.append(self.right.pop())
else:
val = self.right.pop()
print(val)
def size(self, x):
print(len(self.left) + len(self.right))
def empty(self, x):
print(1 if not (self.left or self.right) else 0)
def front(self, x):
if not self.left:
if not self.right:
val = -1
else:
val = self.right[0]
else:
val = self.left[-1]
print(val)
def back(self, x):
if not self.right:
if not self.left:
val = -1
else:
val = self.left[0]
else:
val = self.right[-1]
print(val)
import sys
input=sys.stdin.readline
deque = Deque()
order_dict = {
'push_front' : deque.push_front,
'push_back' : deque.push_back,
'pop_front' : deque.pop_front,
'pop_back' : deque.pop_back,
'size' : deque.size,
'empty' : deque.empty,
'front' : deque.front,
'back' : deque.back
}
for i in range(int(input().strip())):
order = input().strip().split()
order.append('')
order_dict[order[0]](order[1])