题解 | 【模板】队列操作

que, n = [], int(input().strip())
for _ in range(n):
    a = list(map(int, input().strip().split(" ")))
    if a[0] == 1:
        que.append(a[1])
    elif a[0] == 2:
        print("ERR_CANNOT_POP") if not que else que.pop(0)
    elif a[0] == 3:
        print("ERR_CANNOT_QUERY" if not que else que[0])
    elif a[0] == 4:
        print(len(que))