(1)
0 1 -> 1 wait
2 3-> 5 wait print 1
3 4-> 7 wait print 5
.
.
(2)
0 1 ->1  wait
4 5 -> 9 #1 wait
4 5 ->9 #2 wait
4 5 -> 9 #3  wait
2 2 ->4  wait  <- now- printf '1' & print '9' for 3
.
.
(3)
0 1 ->1 wait
4 5 -> 9 #1 wait
4 5 ->9 #2 wait
4 5 -> 9 #3  wait
5 5 ->10  wait <- now- printf 1+1=2 & print '0' for 3
.
.
.

And this my program ,Who can tell why I got WA?
var
  X,Y,save:byte;
  N,I,j,mark:longint;
  start:boolean;
begin
  readln(N);
  mark:=0;start:=true;
  for i:=1 to N do begin
    readln(x,y);
    if start and(x+y=0) then continue
                        else start:=false;
    if mark=0 then begin save:=x+y;inc(mark); end
              else if x+y<9 then begin
                                     write(save);
                                     for j:=1 to mark-1 do write(9);
                                     save:=x+y;mark:=1;
                                 end
                   else if x+y=9 then inc(mark)
                        else begin
                               write(save+1);
                               for j:=1 to mark-1 do write(0);
                               save:=x+y-10;mark:=1;
                             end;
  end;
  write(save);
  for j:=1 to mark-1 do write(9);
  writeln;
end.