program fractii;

var
  n, i,j, z,x,k,m: longint;
  in_f, out_f: text;
  num:real;
  phi: array[1..1000000] of real;
  ok: boolean;

begin
  assign(in_f, 'fractii.in');
  assign(out_f, 'fractii.out');
  reset(in_f);
  
  readln(in_f, n);
  
for i:=1 to n do phi[i]:=i;

for i:=2 to n do
   if (phi[i]=i) then
   begin  
     j:=i;
  
   while j<=n do
     begin
      
     phi[j] := phi[j]/i;
     phi[j] := phi[j]*(i-1);
       j+=i;
      end;
      end;
for i := 1 to n do num:=num+phi[i];
num:=num*2-1;



 

  rewrite(out_f);
  write(out_f, num);
  close(out_f);
  
end.