PROBLEM STATEMENT
Given a string s, its roughness is calculated as follows:  Let c1 be the letter that appears most 
frequently in s, and let c2 be the letter that appears least frequently (c2 must appear at least 
once).  The roughness of s is the number of occurrences of c1 minus the number of occurrences of c2.

You are allowed to modify s by erasing between 0 and n characters, inclusive (see example 1 for 
clarification).  Return the minimum possible roughness that can be achieved by such a modification.

DEFINITION
Class:RoughStrings
Method:minRoughness
Parameters:string, int
Returns:int
Method signature:int minRoughness(string s, int n)


CONSTRAINTS
-s will contain between 1 and 50 characters, inclusive.
-s will contain only lowercase letters ('a'-'z').
-n will be between 0 and m-1, inclusive, where m is the number of characters in s.


EXAMPLES

0)
"aaaaabbc"
1

Returns: 3

We may remove one 'a' or one 'c' to obtain the minimal roughness of 3.

1)
"aaaabbbbc"
5

Returns: 0

One of the ways is to remove 'c' and all occurrences of 'a'.

2)
"veryeviltestcase"
1

Returns: 2



3)
"gggggggooooooodddddddllllllluuuuuuuccckkk"
5

Returns: 3



4)
"zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
17

Returns: 0



5)
"bbbccca"
2

Returns: 0

Sometimes you may want to remove less than n characters.

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