program lol;
var a:array[1..1000000] of boolean;
b:array[1..1000000] of qword;
n,i,j,k,l:longint;f,g:text;m:qword;
begin
assign(f,'fractii.in');
reset(F);
assign(g,'fractii.out');
rewrite(G);
readln(f,n);
a[1]:=true;
for i:=1 to n do
    if not a[i] then
                begin
                j:=i;
                while j+i<=N do
                begin
                j:=j+i;
                a[j]:=true;
                end;
                end;
m:=1;
for i:=2 to n do
       b[i]:=i;
for i:=2 to n do
        if a[i]=false then
                        begin
                        j:=i;
                        while j<=n do
                                   begin

                                   b[j]:=(b[j] div i)*(i-1);
                                   j:=j+i;
                                   end;   end;
for i:=2 to n do
        m:=m+2*b[i];
writeln(g,m);
close(F);
close(G);
end.