program lottery;
var
  n,m,i,j,k:integer;
  t:int64;
  sz:array[0..30,0..30]of int64;
begin
  fillchar(sz,sizeof(sz),0);
  assign(input,'lottery.in');
  assign(output,'lottery.out');
  reset(input);
  rewrite(output);
  readln(n,m);
  for i:=1 to n do
    for j:=1 to m do
    begin
      if i=j then begin
        sz[i,j]:=1;
        for k:=2 to i do
          sz[i,j]:=sz[i,j]*k;
      end
      else begin
        if i>j then sz[i,j]:=0 else begin
          sz[i,j]:=sz[i,j-1]*i+sz[i-1,j-1]*i;
        end;
      end;
    end;
  t:=n;
  for i:=2 to m do
    t:=t*n;
  writeln(sz[n,m]/t:0:4);
  close(input);
  close(output);
end.