题解 | 【模板】队列操作

n = int(input().strip())
queue = []
for _ in range(n):
    num = list(map(int,input().strip().split(" ")))
    if num[0] == 1:
        queue.append(num[1])
    elif num[0] == 2:
        if len(queue) == 0:
            print("ERR_CANNOT_POP")
        else:
            queue.pop(0)
    elif num[0] == 3:
        if queue:
            print(queue[0])
        else:
            print("ERR_CANNOT_QUERY")
    elif num[0] == 4:
        print(len(queue))