program bai1;
var s,i,n:longint;
begin
write('N= '):readln(n);
i:=0;
s:=1;
while i<=n do
begin
if i mod 2=0 then s:=s*1/i;
i:=i+1;
end;
write('S= ',s);
readln
end.
Var i,n:integer;
S:real;
Begin
Write (' nhap n : ');
Readln(n);
S:=1;
While i<=n do S:=S*1/i;
Write (' tong S : ',S:5:6);
Readln;
end.