The task is simple: given any positive integer N, you are supposed to count the total number of 1‘s in the decimal form of the integers from 1 to N. For example, given N being 12, there are five 1‘s in 1, 10, 11, and 12.
Input Specification:
Each input file contains one test case which gives the positive N (<=2^30^).
Output Specification:
For each test case, print the number of 1‘s in one line.
Sample Input:
12
Sample Output:
5
原文：https://www.cnblogs.com/AbsolutelyPerfect/p/9223968.html