Определитель 4х4 нельзя преобразовать тип real к integer

program Kramer;
uses crt;
var a:array [1..4,1..4] of integer;
    b:array [1..4] of integer;
    i,j,k,l:integer;
    d,d1,d2,d3,d4:real;
    x1,x2,x3:integer;
    
begin
clrscr;
writeln('Введите коэффиценты при неизвестных:');
for i:=1 to 4 do
for j:=1 to 4 do
 begin
  write('a[',i,',',j,']=');
  readln(a[i,j]);
 end;
 writeln('Введите свободные члены:');
for i:=1 to 4 do
 begin
  write('b[',i,']=');
  readln(b[i]);
end;
clrscr;
writeln('Расширенная матрица коэффициентов:');
for i:=1 to 4 do
begin
  for j:=1 to 4 do
  write(a[i,j]);
  writeln(b[i]);
end;
writeln;
d1:=a[2,2]*a[3,3]*a[4,4]+a[3,2]*a[4,3]*a[2,4]+a[2,3]*a[3,4]*a[4,2]-a[2,4]*a[3,2]*
a[4,2]-a[3,2]*a[2,3]*a[4,4]-a[4,3]*a[3,4]*a[2,2];
d2:=a[1,2]*a[3,3]*a[4,4]+a[3,2]*a[4,3]*a[1,4]+a[1,3]*a[3,4]*a[4,2]-a[1,4]*a[3,2]*
a[4,2]-a[3,2]*a[1,3]*a[4,4]-a[4,3]*a[3,4]*a[1,2];
d3:=a[1,2]*a[2,3]*a[2,4]+a[1,3]*a[2,4]*a[4,2]+a[2,2]*a[4,3]*a[1,4]-a[1,4]*a[2,3]*
a[4,2]-a[2,2]*a[1,3]*a[4,4]-a[4,3]*a[2,4]*a[1,2];
d4:=a[1,2]*a[2,3]*a[3,4]+a[1,3]*a[2,4]*a[3,2]+a[2,2]*a[3,3]*a[1,4]-a[1,4]*a[2,3]*
a[3,2]-a[2,2]*a[1,3]*a[3,4]-a[2,4]*a[3,3]*a[1,2];
d:=a[1,1]*d1-a[2.1]*d2+a[3,1]*d3-a[4,1]*d4;
if d=0 then
 begin
  write('Матрица линейно зависима');
  readln;
  exit
 end;
 writeln(d);
 end.

for i:=1 to 4 do
begin
  for j:=1 to 4 do
  write(a[i,j]:4);
  writeln(b[i]:6);
end;