#!/bin/bash


head=$1
while [ ${#head} -gt 3 ]; do
   tail=${head: -3}
   head=${head:0: -3}
   if [ -z ${result} ]; then
      result=${tail}
   else
      result="${tail},${result}"
   fi
   if [ ${#head} -le 3 ]; then
      result="${head},${result}"
   fi
done
echo ${result}