# your code goes here
def f(str,i,j)
	a=str[i]
	b=str[j]
	str[j]=a
	str[i]=b
	return str.to_i
end
str=STDIN.gets.chomp
ans=0
str.size.times do |i|
	str.size.times do |j|
		ans=[ans,f(str,i,j)].max
	end
end

puts ans