require 'prime'

def f(n)
	re=0
	n.to_s.chars{|e|
		re+=e.to_i
	}
	return re
end

d=gets.to_i
u=gets.to_i
x=Prime.each(u).to_a
while x[0]<d
	x.shift
end

x=x.map{|e|
	e2=e
	while e2>9
		e2=f(e2)
	end
	[e,e2]
}
anslen=1
ans=x[0]
while x.empty? == false
	e=x.shift
	e0=e[0]
	e1=e[1]
	hs={}
	hs[e1]=0
	len=1
	x.each{|e2|
		if hs.key?(e2[1])==false
			len+=1
			hs[e2[1]]=0
		else
			break
		end
	}
	if anslen<=len
		ans=e0
		anslen=len
	end
end
puts ans