Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
The ATK of this card is the combined Levels of all face-up monsters you control x 300.
--ザ・カリキュレーター
--The Calculator
local s,id=GetID()
function s.initial_effect(c)
	--attack
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_SET_ATTACK)
	e1:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
	e1:SetRange(LOCATION_MZONE)
	e1:SetValue(s.atkval)
	c:RegisterEffect(e1)
end
function s.atkval(e,c)
	local g=Duel.GetMatchingGroup(Card.IsFaceup,c:GetControler(),LOCATION_MZONE,0,nil)
	return g:GetSum(Card.GetLevel)*300
end