from collections import deque import sys list = deque() n = int(sys.stdin.readline()) for i in range(n): t = sys.stdin.readline().rstrip().split() if t[0] == 'push_back': list.append(t[1]) if t[0] == 'push_front': list.appendleft(t[1]) if t[0] == 'pop_front': if len(list) == 0: print(-1) else: print(list.popleft()) if t[0] == 'pop_back': if len(list) == 0: print(-1) else: print(list.pop()) if t[..