program Project14;
{$APPTYPE CONSOLE}
var i,n1,N,Znak:integer;D,D1:real;
begin
writeln('Vvedit chyslo N');
readln(N);
Znak:=-1;D1:=1;
for n1:=2 to 2*N do begin
Znak:=Znak*(-1);
D:=-1*(Znak/n1);D1:=D1*D;end;
writeln('Dobutok D=',D1:1:17);
readln;
end.