program zhonhgjiangdejilv;var
  i,j,n,m:integer;
  f:array[1..20,0..20]  of longint;
  t:int64;
  p:real;
begin
  assign (input,'lottery.in');
  reset (input);;
  assign (output,'lottery.out');
  rewrite (output);
    readln (n,m);
    for i:=1 to m do
      f[1,i]:=1;
    for i:=2 to n do
      for j:=1 to m do
        if i>j then
          f[i,j]:=0
        else
          f[i,j]:=f[i,j-1]*i+f[i-1,j-1]*i;
    t:=1;
    for i:=1 to m do
      t:=t*n;
    p:=f[n,m]/t;
    writeln (p:0:4);
  close (input);
  close (output)
end.