#!/bin/sh

CTL="/sys/class/backlight/intel_backlight/brightness"

_old=$(cat $CTL)

if [ ${_old} -ge 200 ]; then
	_dec=20
elif [ ${_old} -ge 100 ]; then
	_dec=10
elif [ ${_old} -ge 50 ]; then
	_dec=5
elif [ ${_old} -ge 20 ]; then
	_dec=3
elif [ ${_old} -ge 10 ]; then
	_dec=2
elif [ ${_old} -gt 1 ]; then
	_dec=1
else
	exit 0
fi
	
echo $((${_old}-${_dec})) > $CTL