bash : expression recursion level exceeded

I'm a newbie to bash scripting and trying to do some exercises. Getting error like this when I'm trying to stop the program with "finish" string.: line 9: ((: finish: expression recursion level exceeded (error token is "finish"). What is the problem? Also I'd like to learn my other faults. And my program is :

#!/bin/bash
number=0
finish="finish"
temp=0
echo "Enter a number."
while true;
do
    read -r number
    if (( $number > $temp ))
    then
        temp=$number
    fi
    if [[ $number == $finish ]]
    then 
       break
    fi
done    
echo "Largest : $temp"