i think, in your program u must not let IND reach the value
81, this means whenever it gets to 80, u must immediately
give make it 0 (ind:=0).
Secondly, bout the variable MAXPOS, whenever you update the
varibale IND, u must compare MAXPOS with IND
( if MAXPOS < IND then MAXPOS:=IND )
because IND never reach to 81, ie IND <= 80 so MAXPOS <= 80
too, that all i can explain to you.
btw, i've changed your source code with the above thing, and
get AC with it.
Here is the your changed source

var a:array[1..20000] of char;
    i,j,ind,n,n2,maxpos:integer;
    c:char;
begin
   ind:=0;  n:=0; n2:=0;
   for i:=1 to 20000 do a[i]:=' ';maxpos:=0;
   while not eof do
   begin
      inc(n2);
      while not eoln do
      begin
         inc(n); read(c);
         if c='>' then

{begin changing here}

begin
inc(ind);
if ind > maxpos then maxpos:=ind;
if ind = 80 then ind:=0;
end

{stop changing here}

         else
          if c='<' then
          begin  if ind>0 then dec(ind)  end
          else
            begin
               inc(ind);
               a[ind]:=c;

{here's another change}

if ind > maxpos then maxpos:=ind;
if ind = 80 then ind:=0;

{stop of change}
            end;
      end;
      readln;
   end;
   for i:=1 to maxpos do write(a[i]);
end.

=> Got AC with time = 0.02sec ;)

Ah, btw, why is your A array is to big, you only need it
[1..80], and what about the variable "n2", i don't know you
use it for what :-/

Good luck !

QH@