Integer? float? confused...

["WM" <wwminirl@hotmail.com>]

I have written a program to calculate Sin. The compiler(AdaGIDE 6.23) said:
"expected type standard.float", why? Please piont out errors, Thanks.

with Ada.Text_Io, Ada.Integer_Text_Io,Ada.Float_Text_Io;
use Ada.Text_Io, Ada.Integer_Text_Io,Ada.Float_Text_Io;

procedure sin is
   sin_result : float;
   i : integer;
   function Calc_Sin (Num : Integer) return float is
      begin
         Sin_Result := Num - (Num ** 3) / 6 + (Num ** 5) / 120;
         return Sin_Result;
   end Calc_Sin;

begin

put("input int: ");
get(i);
Sin_Result := Calc_Sin(Num=>i);
Put(Item=>Sin_Result, Fore=>1, Aft=>4, Exp=>0);

end sin;