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A Loaf of Almond Cherry Bread

"Please don't put almonds into bread, especially cherry bread!"

Input: A string of "a", "b", "c".
Output: A binary number, the tastiness point of the most tasty sub-string (or maybe, sub-bread).
Each "b" provides 1 point and each "c" provides -1 point. Any "a" should be avoided.
Constraint: 1 <= Input length <= 7
Input contains at least one "b".