def bb
	n = gets.chomp.to_i
	if    n <=      9 then puts n
	elsif n <=     99 then puts 9
	elsif n <=    999 then puts 9 +   n-100+1
	elsif n <=   9999 then puts 9 + 999-100+1
	elsif n <=  99999 then puts 9 + 999-100+1 +     n-10000+1
	elsif n <= 999999 then puts 9 + 999-100+1 + 99999-10000+1
#	elsif n <= 100000 then puts 90909
	end
end

bb