{$n+} 
program fractiii; 
type vector=array[1..2000000] of record
x:boolean; 
l,k:longint;end; 
var a:vector; 
n,z,i,j,p,p1:longint; 
t:boolean; 
s,s1,s2,s3:extended; 
f,g:text; 
begin 
assign(f,'fractii.in');assign(g,'fractii.out');reset(f);rewrite(g); 
read(f,n); 
for i:=2 to n do begin 
z:=i;if a[i].x=false then begin a[i].l:=(i-1)*2;s1:=a[i].l; s:=s+s1;end 
else begin s1:=a[i].l;s2:=a[i].k;s3:=i; 
s:=s+(((s1*s3)/ s2)*2);end; 
while z<n do begin 
if (z mod 2<>0) and (i>2) then begin
z:=z+i;
a[z].x:=true;t:=true;
if a[z].l=0 then begin a[z].l:=1;a[z].k:=1;end;
if a[i].x=false then begin a[z].l:=a[z].l*(i-1);a[z].k:=a[z].k*i;end;
end;end;end;
s:=s+1;write(g,s:0:0);close(f);close(g);end.