Staircase Numbers (APCS 2018-02 Expert)

2.0s 256M

A positive integer is a staircase number when its decimal digits never decrease from left to right, such as \(9,112,777\). Count staircase numbers at most \(N\). Leading zeros are forbidden and zero is excluded.

Input Format

Read an integer \(N\).

Output Format

Print the count.

Constraints

\(1\le N\le10^{18}\).

Sample Input 1

25

Sample Output 1

22

Sample Input 2

101

Sample Output 2

54

Source

APCS 2018-02 public archive version: tcirc:d080。

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