a,b = gets.chomp.split
l_a,l_b = [a,b].map(&:length)
if l_a > l_b
    puts a
elsif l_a < l_b
    puts b
else
    l_a.times{|i|
        if a[i] == b[i]
            next
        end
        if [a[i],b[i]].sort == ['4','7']
            if a[i] == '4'
                puts a
            else
                puts b
            end
        else
            if a[i] > b[i]
                puts a
            else
                puts b
            end
        end
        break
        }
      
end