puts gets.split.max{|a,b|

a=a.reverse
b=b.reverse
c=a.size<=>b.size
if c!=0
c
else
(0...a.size).each{|i|c=a[i]=='4'&&b[i]=='7' ? 1 : a[i]=='7'&&b[i]=='4' ? -1 : a[i]<=>b[i];break if c!=0}
c
end
}[1]