a, b = gets.chomp.split(' ')

a_size = a.size
b_size = b.size

if a_size > b_size
  puts a
  exit
elsif a_size < b_size
  puts b
  exit
end

0.upto(a_size - 1) do |i|
  if a[i] == '4' && b[i] == '7'
    puts a
    exit
  elsif a[i] == '7' && b[i] == '4'
    puts b
    exit
  elsif a[i] > b[i]
    puts a
    exit
  elsif a[i] < b[i]
    puts b
    exit
  end
end

puts a