unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    GroupBox1: TGroupBox;
    Label1: TLabel;
    Edit1: TEdit;
    Label2: TLabel;
    Edit2: TEdit;
    procedure Edit1Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
function pi(k:integer):real;
var t:integer;
a,b,e,s:real;
begin
t:=3;
s:=0;
a:=1;
b:=1;
e:=exp(k*ln(0.1));
while a>=e do
  begin
     while b<t do
     begin
       a:=a*b/(b+1);
       b:=b+2;
     end;
     b:=1;
     s:=s+a/(t*exp(t*ln(2)));
     t:=t+2;
  end;
  pi:=6*(1/2+s);
end;
procedure TForm1.Edit1Change(Sender: TObject);
var k:integer;
    m:string;
    c:real;
begin
if edit1.Text='' then edit1.Text='5'
k:=strtoint(edit1.text);
c:=pi(k);
m:=format('%20.18f',[c]);
edit2.Text:=copy(m,0,k+2);

end;

end.