function f(n: longint): longint;
var
i, t: longint;
begin
if n = 1 then
f := 2
else
begin
t := 1;
for i := n to 2 * n do
t := t * i;
f := f(n - 1) + t;
end;
end;
function f(n: longint): longint;
var
i, t: longint;
begin
if n = 1 then
f := 2
else
begin
t := 1;
for i := n to 2 * n do
t := t * i;
f := f(n - 1) + t;
end;
end;