program fac;
var f:text;
n,i,j,nr:longint;
phi:array[1..1000000] of int64;
begin
 assign(f,'fractii.in'); reset(f);
 readln(f,n);
 close(f);
 for i:=1 to n do
  phi[i]:=i;
 nr:=1;
  for i:=2 to n do begin
   if phi[i]=i  then  begin
     j:=i;
      while j<=n do begin
       phi[j]:=phi[j] div i *(i-1);
       inc(j,i);
      end;
      end;
      nr:=nr+2*phi[i];
  end;

 assign(f,'fractii.out'); rewrite(f);
 writeln(f,nr);
 close(f);
end.