func main()
	var n: int :: cui@inputInt()
	var x: int :: 10
	var ans: int :: 0
	for i(1, 100000)
		if(i = x)
			do x :* 10
		end if
		if(i * x ^ 2 + i * x + i > n)
			break i
		end if
		do ans :+ 1
	end for
	do cui@print("\{ans}\n")
end func