str = gets.to_s.split
a = str[0]
b = str[1]
if a.length < b.length then
    puts b 
elsif a.length > b.length then
    puts a
else
    a.length.times do |i|
        if a[i] == "4" && b[i] == "7" then
            puts a
            break
        elsif a[i] == "7" && b[i] == "4" then
            puts b
            break
        elsif a[i] < b[i] then
            puts b
            break
        elsif a[i] > b[i] then
            puts a
            break
        end
    end
end