#!/usr/bin/env crystal
lib C;fun strtoll(s: UInt8*,p: UInt8*,b: Int32): Int64;end
starting=1_i64
base=10
while (s=gets)!=nil
	n=C.strtoll(s.not_nil!,nil,10)+starting-2
	digits=1_i64
	expbase=1_i64
	while (x=digits*expbase*(base-1))<=n
		digits+=1
		expbase*=base
		n-=x
	end
	num=expbase+n//digits
	d=digits-1-n%digits
	d.times{num//=base}
	puts num%base
end