You are given an integer `n`.

Each number from `1` to `n` is grouped according to the sum of its digits.

Return the number of groups that have the largest size.

Example 1:

    Input: n = 13
    Output: 4
    Explanation: There are 9 groups in total, they are grouped according sum of its digits of numbers from 1 to 13:
    [1,10], [2,11], [3,12], [4,13], [5], [6], [7], [8], [9].
    There are 4 groups with largest size.

Example 2:

    Input: n = 2
    Output: 2
    Explanation: There are 2 groups [1], [2] of size 1.

Constraints:

- `1 <= n <= 104`