VAR
 N,i:Integer;
 a,S,x:Real;

BEGIN
 Write('N= ');
 Readln(N);
 Write('x= ');
 Readln(x);
 a:=1;
 S:=a;
 For i:=1 to N do
  begin
   a:=-a/i*(i+2)*x;
   S:=S+a;
  end;
 Writeln('S= ',S:0:3);
 Readln;
END.