### 738. Monotone Increasing Digits

Given a non-negative integer N, find the largest number that is less than or equal to N with monotone increasing digits.

(Recall that an integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y.)

Example 1:

Input: N = 10
Output: 9


Example 2:

Input: N = 1234
Output: 1234


Example 3:

Input: N = 332
Output: 299


Note: N is an integer in the range [0, 10^9].

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