procedure getSum(x: double; n: integer; var ans: double);
var
  i: integer;
  x2, prev: double;
begin
  if (x = 0) or (n < 1) then
  begin
    ans := 0;
    exit;
  end;
  x2 := x * x;
  prev := x;
  ans := x;
  for i := 2 to n do
  begin
    prev := -prev * x2 * (2 * i - 1) / i / (2 * i - 3);
    ans := ans + prev;
  end;
end;

var
  x, answer: double;
  n: integer;

begin
  readln(x, n);
  getSum(x, n, answer);
  writeln(answer);
end.