var n,i,j,nr:longint;
    a:array[1..1000000] of 0..1;
    f,g:text;
procedure ciur;
begin
for i:=2 to trunc(sqrt(n div 2+1)) do
  if a[i]=0 then begin
    j:=sqr(i);
    while j<=n do begin
      a[j]:=1;
      j:=j+i;
    end;
  end;
end;
begin
assign(f,'fractii.in'); reset(f);
assign(g,'fractii.out'); rewrite(g);
read(f,n);
ciur;
nr:=0;
for i:=2 to n div 2+1 do if a[i]=0 then nr:=nr+(n div i-1)*(n div i) div 2;
nr:=(n*(n-1) div 2-nr)*2+1;
write(g,nr);
close(g);
end.