The 10-digit International Standard Book Number (ISBN-10) a1a2a3a4a5a6a7a8 a9a10 has the property (a1, a2, . . . , a10) ⋅ (10, 9, 8, 7, 6, 5, 4, 3, 2, 1) mod 11 = 0. The digit a10 is the check digit. When a10 is required to be 10 to make the dot product 0, the character X is used as the check digit. Verify the check digit for the ISBN-10 assigned to this book.
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