$6174$ is the Kaprekar constant. All natural numbers less than $10,000($except some with same digits$)$ can be reduced to $6174$ in the following steps:

Order the digits of the number in descending and ascending order and compute the difference. Repeat the process till you get $6174.$

Example

n $=2376$

Digits in descending order $=7632$

Digits in ascending order $=2367$

Step$1$