a,b=STDIN.gets.chomp.split(" ")
if a.size()!=b.size() then
	if a.size()>b.size() then
		puts a
	else
		puts b
	end
else
	a.size().times do |i|
		p=i
		if (a[p]=="7") && (b[p]=="4") then
			puts b
			break
		elsif (a[p]=="4") && (b[p]=="7") then
			puts a
			break
		elsif a[p]<b[p] then
			puts b
			break 
		elsif a[p]>b[p] then
			puts a
			break 
		end
	end
end