Вычислить среднее арифметическое четырех угловых чисел массива

unit Unit2;
 
interface
 
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
 
type
TForm2 = class(TForm)
Button1: TButton;
Label1: TLabel;
Edit1: TEdit;
Edit2: TEdit;
Label2: TLabel;
Label3: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
 
var
Form2: TForm2;
 
implementation
 
{$R *.dfm}
 
procedure TForm2.Button1Click(Sender: TObject);
const nmax=15;
var a:array [1..nmax,1..nmax] of integer;
b,c,k:integer;
i,j:byte;
x:real;
begin
randomize;
repeat
b:=StrToInt(Edit1.Text);
until b in [1..nmax];
repeat
c:=StrToInt(Edit2.Text);
until c in [1..nmax];
for i:=1 to b do
begin
for j:=1 to c do
begin
a[i,j]:=random(100);
end;
end;
//for i:=1 to nmax do
//Label4.Caption:=label4.caption+FloatToStr(a[b]);
//Label4.Caption:=label4.caption+FloatToStr(a[c]);
//Label4.caption:=label4.caption+#13;
//form2.Caption:='Massiv'+IntToStr(a[i,j]);
x:=(a[1,1] + a[1,10] + a[10,1] + a[10,10])/4;
Label3.Caption:='результат'+FloatToStr(x);
readln(x);
end;
 
end.

repeat
b:=StrToInt(Edit1.Text);
until b in [1..nmax];

var a:array of array of integer;

const n=10;
var a:array[1..n,1..n] of integer;