11. If in any permutation of $1,2,3, \cdots, 18$, there always exists a sum of 6 consecutive numbers not less than $m$, then the maximum value of the real number $m$ is $\qquad$.
In the arbitrary permutation of $1,2,3, \cdots, 18$, if we group every 6 consecutive numbers from left to right, we will have three groups. Since the sum of the three groups is $\frac{18 \times 19}{2}=3 \times 57$, by the pigeonhole principle, there must be at least one group whose sum is not less than 57, i.e., $m \geqslant 57$.
Arrange $1,2,3, \cdots, 18$ as $18,1,17,2,16,3,15,4,14,5,13,6,12,7,11,8,10,9$, in this case, the sum of any 6 consecutive numbers does not exceed 57. Therefore, the maximum value of the real number $m$ is 57.