program fractii;
var
 s:longint;
 n,i,j:integer;
 v:array[1..10000] of integer;
 fin,fout:text;
begin
 assign(fin,'fractii.in');
 reset(fin);
 readln(fin,n);
 close(fin);
 for i:=1 to n do
  v[i]:=i;
 for i:=2 to n do
  if v[i]=i then
   begin
    j:=2*i;
    while j<=n do
     begin
      v[j]:=v[j] div i;
      j:=j+i;
     end;
   end;
 s:=1;
 for i:=2 to n do
  s:=s+(v[i]-1)*2;
 assign(fout,'fractii.out');
 rewrite(fout);
 writeln(fout,s);
 close(fout);
end.