True monochromization with Pascal

(*) my best version.. the

var
f1: file of char;
f2: file of char;
i: longint;
j: longint;
ch:char;
a:char;
b:char;
c:char;

begin
assign(f1,’xxx.raw’);
reset(f1);
assign(f2,’out2.raw’);
rewrite(f2);

j:=filesize(f1) div 3;

for i:=1 to j do
begin
read(f1,a);
read(f1,b);
read(f1,c);
ch:=chr(ord(a) div 3 + ord(b) div 2 + ord(c) div 17);
write(f2,ch);
end;

close(f1);
close(f2);
end.