题目描述
Problem Statement
For a positive integer n, let us define f(n) as the number of digits in base 10.
You are given an integer S.
Count the number of the pairs of positive integers $(l, r) (l \leq r)$ such that f(l) + f(l + 1) + ... + f(r) = S, and find the count modulo 10^9 + 7.
Input
Input is given from Standard Input in the following format:
S
Output
Print the answer.
Constraints
- $1 \leq S \leq 10^8$
Sample Input 1
1
Sample Output 1
9
There are nine pairs (l, r) that satisfies the condition: (1, 1), (2, 2), ..., (9, 9).
Sample Input 2
2
Sample Output 2
98
There are 98 pairs (l, r) that satisfies the condition, such as (1, 2) and (33, 33).
Sample Input 3
123
Sample Output 3
460191684
Sample Input 4
36018
Sample Output 4
966522825
Sample Input 5
1000
Sample Output 5
184984484
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分