Есть код, нужно переделать через Function

program ploshad;
 
{$APPTYPE CONSOLE}
 
uses
SysUtils;
var x,y,z,t:integer;
S1,S2,S,a,b:double;
 
begin
writeln ('vvod x ');
readln(x);
if x<=0 then write ('error');
writeln ('vvod y ');
readln(y);
if y<=0 then write ('error');
writeln ('vvod z ');
readln(z);
if z<=0 then write ('error');
writeln ('vvod t ');
readln(t);
if t<=0 then write ('error');
 
a:=(sqrt((x*x)+(y*y)));
b:=((a+t+z)/2);
S1:=(x*y)/2;
S2:=sqrt(b*(b-a)*(b-t)*(b-z)); \\через формулу Герона
S:=S1+S2;
writeln ('S=', S:2:2);
readln;
end.

function SquareFour(x, y, z, t: integer): double;
var
  S1, S2, a, b: double;
begin
  a := (sqrt((x * x) + (y * y)));
  b := ((a + t + z) / 2);
  S1 := (x * y) / 2;
  S2 := sqrt(b * (b - a) * (b - t) * (b - z)); //через формулу Герона
  SquareFour := S1 + S2;
end;
 
var
  x, y, z, t: integer;
 
begin
  writeln('vvod x ');
  readln(x);
  if x <= 0 then write('error');
  writeln('vvod y ');
  readln(y);
  if y <= 0 then write('error');
  writeln('vvod z ');
  readln(z);
  if z <= 0 then write('error');
  writeln('vvod t ');
  readln(t);
  if t <= 0 then write('error');
 
  writeln('S=', SquareFour(x, y, x, t): 2: 2);
  readln;
end.

function get(s : string) : integer;
var value : integer;
begin
  writeln('vvod ', s);
  readln(value);
  if value <= 0 then write('error');
  get := value;
end;
 
function SquareFour(x, y, z, t: integer): double;
var
  S1, S2, a, b: double;
begin
  a := (sqrt((x * x) + (y * y)));
  b := ((a + t + z) / 2);
  S1 := (x * y) / 2;
  S2 := sqrt(b * (b - a) * (b - t) * (b - z));
  SquareFour := S1 + S2;
end;
 
begin
  writeln('S=', SquareFour(get('x'), get('y'), get('z'), get('t')): 2: 2);
  readln;
end.