import sys from collections import deque N = int(input()) Queue = deque([]) for _ in range(N): line = sys.stdin.readline().split() if line[0] == "push": Queue.append(line[1]) elif line[0] == "pop": if not Queue: print(-1) else: print(Queue.popleft()) elif line[0] == "front": if len(Queue) > 0: print(Queue[0]) else: print(-1) elif line[0] == "back": if len(Queue) > 0: print(Queue[-1]) else: print..