Matrix op. №4 refined

program Mx_4;
type MyArray=array of array of Integer;
var a,b:MyArray;
  i,j,m,n:Word;

procedure PullArray(var a:MyArray; var m,n:Word);
var Fin:Text;
  i,j:Word;
begin
  Assign(Fin,'in.txt');
  ReSet(Fin);
  ReadLn(Fin,m,n); // array size
  SetLength(a,m+1,n+1);
  for i:=1 to m do
  begin
    for j:=1 to n do
      Read(Fin,a[i,j]);
    ReadLn(Fin);
  end;
  Close(Fin);
end;

function Compute(a:MyArray; m,n:Word; y,x:Word; mode:Integer):Integer;
var i,i1,i2,j,j1,j2:Word;
  s:Integer;
begin
  if mode=1 then begin //down-right
       i1:=y+1;
  j1:=x+1;  j2:=n;
       i2:=m;
  end else begin //upper-left
       i1:=1;
  j1:=1;  j2:=x-1;
       i2:=y-1;
  end;
  s:=0;
  for i:=i1 to i2 do
    for j:=j1 to j2 do
      s:=s+a[i,j];
  Compute:=s;
end;

procedure PushArray(b:MyArray; m,n:Word);
var i,j:Word;
  Fout:Text;
begin
  Assign(Fout,'out.txt');
  ReWrite(Fout);
  WriteLn(Fout,m,' ',n);
  for i:=1 to m do
  begin
    for j:=1 to n do
      Write(Fout,b[i,j]:4,' ');
    WriteLn(Fout);
  end;
  Close(Fout);
end;
//main
begin
  PullArray(a,m,n);
  SetLength(b,m+1,n+1);
  for j:=1 to ((n+1) div 2) do
    for i:=1 to m do
      b[i,j]:=Compute(a,m,n,i,j,1);
  for j:=((n+1) div 2 +1) to n do
    for i:=1 to m do
      b[i,j]:=Compute(a,m,n,i,j,2);
  PushArray(b,m,n);
end.