Determine if the characters in a string are in non-decreasing alphabetical order.

Examples

Example 1

Input:  "abc"
Output: true

Example 2

Input:  "aab"
Output: true

'a' ≤ 'a' ≤ 'b' (non-decreasing)

Example 3

Input:  "ba"
Output: false

Example 4

Input:  ""
Output: true

Empty string is considered ordered

Constraints

• Empty strings and single characters are considered ordered
• Repeating characters are allowed (non-decreasing)