program liumohan;
var n,i,j,x,c:longint; s:string;
begin
  read(n);
  for i:=1 to n do
  begin
  c:=0;
    str(i,s);
    for j:=1 to length(s) do
    if (s[j]='0') and (c=0) then
    begin
      x:=x+1;
      c:=1;
      end;
      end;
      writeln(x);
      end.
/**************************************************************
	Problem: 1750
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/