Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
Cannot be Normal Summoned/Set. Must be Special Summoned (from your hand) by sending 3 other monsters from your hand to the Graveyard, and cannot be Special Summoned by other ways. This card's ATK becomes the combined original Levels of the sent monsters x 300.
--モンタージュ・ドラゴン
--Montage Dragon
local s,id=GetID()
function s.initial_effect(c)
	c:EnableReviveLimit()
	--cannot special summon
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE+EFFECT_FLAG_UNCOPYABLE)
	e1:SetCode(EFFECT_SPSUMMON_CONDITION)
	e1:SetValue(aux.FALSE)
	c:RegisterEffect(e1)
	--special summon
	local e2=Effect.CreateEffect(c)
	e2:SetDescription(aux.Stringid(id,1))
	e2:SetType(EFFECT_TYPE_FIELD)
	e2:SetCode(EFFECT_SPSUMMON_PROC)
	e2:SetProperty(EFFECT_FLAG_UNCOPYABLE)
	e2:SetRange(LOCATION_HAND)
	e2:SetCondition(s.spcon)
	e2:SetTarget(s.sptg)
	e2:SetOperation(s.spop)
	c:RegisterEffect(e2)
end
function s.filter(c,tp)
	return c:IsMonster() and c:IsAbleToGraveAsCost()
end
function s.spcon(e,c)
	if c==nil then return true end
	local tp=c:GetControler()
	local rg=Duel.GetMatchingGroup(s.filter,tp,LOCATION_HAND,0,e:GetHandler())
	return aux.SelectUnselectGroup(rg,e,tp,3,3,aux.ChkfMMZ(1),0,c)
end
function s.sptg(e,tp,eg,ep,ev,re,r,rp,c)
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_DISCARD)
	local rg=Duel.GetMatchingGroup(s.filter,tp,LOCATION_HAND,0,e:GetHandler())
	local g=aux.SelectUnselectGroup(rg,e,tp,3,3,aux.ChkfMMZ(1),1,tp,HINTMSG_DISCARD,nil,nil,true)
	if #g>0 then
		g:KeepAlive()
		e:SetLabelObject(g)
		return true
	end
	return false
end
function s.spop(e,tp,eg,ep,ev,re,r,rp,c)
	local g=e:GetLabelObject()
	if not g then return end
	Duel.SendtoGrave(g,REASON_COST)
	local sum=0
	local tc=g:GetFirst()
	for tc in aux.Next(g) do
		local lv=tc:GetLevel()
		sum=sum+lv
	end
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_SET_ATTACK)
	e1:SetValue(sum*300)
	e1:SetReset(RESET_EVENT|RESETS_STANDARD_DISABLE&~RESET_TOFIELD)
	c:RegisterEffect(e1)
	g:DeleteGroup()
end