3. Fill the numbers $1,2, \cdots, 36$ into a $6 \times 6$ grid, with each cell containing one number, such that the numbers in each row are in increasing order from left to right. The minimum value of the sum of the six numbers in the third column is $\qquad$
$(2015$, National Junior High School Mathematics League Competition)
Hint: Just sort the first three columns in ascending order per row, the sum of the six numbers filled in the third column is
$$
3+6+9+12+15+18=63 \text {. }
$$