program p1;
var k,i,j,n,s:longint;
    a:array[1..100]of longint;
    f1,f2:text;

begin
assign(f1,'fractii.in'); reset(f1);
assign(f2,'fractii.out'); rewrite(f2);

  read(f1,n);

  inc(s);
  for i:=1 to n do
   a[i]:=i;

  for i:=2 to n do
   begin
    if a[i]=i then
               begin
                j:=i;
                while j<=n do
                 begin
                  a[j]:=a[j] div i;
                  a[j]:=a[j] * (i-1);
                  inc(j,i);
                 end;
               end;
   end;

  for i:=2 to n do
   s:=s+a[i]*2;

  write(f2,s);

close(f1); close(f2);
end.