COCI '13 Contest 3 #5 Parovi

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Points: 12 (partial)
Time limit: 1.0s
Memory limit: 64M

Problem type

The distance between two integers is defined as the sum of the absolute result of subtracting their digits. For example, the distance between the numbers 4561 and 3278 is |4-3| + |5-2| + |6-7| + |1-8| = 12. If one of the numbers consists of fewer digits than the other, we fill it with leading zeroes. Therefore, the distance between the numbers 32 and 5678 is |0-5| + |0-6| + |3-7| + |2-8| = 21.

You are given two integers A and B. Calculate the sum of distances between each pair of numbers belonging in the interval [A, B].

Input Specification

The first and only line of input contains integers A, B (1 \le A \le B \le 10^{50\,000}).

Output Specification

The first and only line of output must contain the required number from the text. Given that the number could be extremely large, output the answer modulo 1\,000\,000\,007.

Scoring

In test cases worth 20\% of total points, A and B will not exceed 10\,000.

In test cases worth 40\% of total points, A and B will not exceed 10^{100}.

Sample Input 1

1 5

Sample Output 1

40

Sample Input 2

288 291

Sample Output 2

76

Explanation for Sample Output 2

The distances are, respectively, (288, 289) = 1, (288, 290) = 9, (288, 291) = 8, (289, 290) = 10, (289, 291) = 9, (290, 291) = 1. Each of them counts twice, which is in total 2 \times (1+9+8+10+9+1) = 76.

Sample Input 3

1000000 10000000

Sample Output 3

581093400

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