var f,g:text;
    x,y,i,j,n,s:longint;


BEGIN
assign(f,'fractii.in');reset(f);
assign(g,'fractii.out');rewrite(g);
read(f,n);
close(f);
s:=2*n-1;
for i:=2 to n do
for j:=2 to n do
if (j-i=1)or(i-j=1) then inc(s);

write(g,s);
close(g);
end.