def sgets = gets.strip
def get_int = Integer(sgets)
def get_list = sgets.split
def get_int_list = get_list.map { Integer(_1) }
def puts_yn(b) = puts(b ? 'Yes' : 'No')

n = get_int 
GOOD = [4,5]
m = n.downto(4).find do |i|
  i.digits(10).all? do |j|
    GOOD.include?(j)
  end
end

puts m