The number $839$ can be written as $19q+r$ where $q$ and $r$ are positive integers. What is the greatest possible value of $q-r$?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The number $839$ can be written as $19q+r$ where $q$ and $r$ are positive integers. What is the greatest possible value of $q-r$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
41
The number $839$ can be written as $19q+r$ where $q$ and $r$ are positive integers. What is the greatest possible value of $q-r$?
train