Given a String S (in lowerCase only). Starting from letter 'a' which is the only source. for example:- "aaabcahd..." . Now you can only jump from one character to another in the form that a to b; b to c; c to d and so on. You have to find the maximum distance from source to destination. And if there is no place to jump on then print -1.

Example 1:
Input: aaabcb
Output: 6
Explanation: As 'a' will only jump to 'b'
and the maximum distance will is 6.
Example 2:
Input: aabac
Output: 5
Explanation: As 'a' will only jump to 'b'
and 'b' will jump to 'c' and distance
is 5.

Your Task:
You don't need to read input or print anything. Your task is to complete the function maximum_distance() which takes the string S as input parameter and returns the maximum distance. If not possible to reach at destination then return -1.
Expected Time complexity: O(n)
Expected Space complexity: O(n)

Constraints:
1 <= size of string <= 1000

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