题解 | #【模板】队列#

n = int(input())
queue = []
for i in range(n):
    res = input().split()
    option = res[0] # res[0]是操作 res[1]是操作数
    if option == 'push':
        queue.append(res[1])
    elif option == 'pop':
        # 队列就是ls[0] 栈就是ls[-1]
        print(queue.pop(0) if len(queue) != 0 else 'error')
    elif option == 'front':
        print(queue[0] if len(queue) != 0 else 'error')