n = int(input()) from collections import deque q = deque() for _ in range(n): a = input().split() if a[0] == '1': q.append(int(a[1])) elif a[0] == '2': if q: q.popleft() else: print('ERR_CANNOT_POP') elif a[0] == '3': if q: print(q[0]) else: print('ERR_CANNOT_QUERY') elif a[0] == '4': print(len(q))