> Yes,I admit that hard work is necessary and important,but
> for this single problem 1077,I thoght the algorithm for a
> whole day,nothing valuable was found.I must say that
> efficency is also need to be attached importance to.I
wish
> somebody with kindness and eagerness will help me,I'll
> thank him(or her) a lot.
>

Then it turned out that he forgot to initialize some
vasriable. So his program worked on his machine and did not
work here.

> There's some suxx.
> I've got 'accepted' for this problem at our institute ACM
training (AFAIK there's the same tests), but here's WA.
What can be wrong?

Моэет Анрдрей не может нормально скачать тесты?
May be he is a LAMER?!!
  =)

>

const
     fi         =       '';
     fo         =       '';
     maxn       =       100;
type
    dt          =       record
      d,c       :       longint;
    end;
var
   f,g          :       text;
   n            :       longint;
   a            :       array[1..maxn] of dt;
   d            :       array[1..maxn] of longint;
   truoc        :       array[1..maxn] of longint;
   max          :       longint;
   li           :       longint;

procedure nhap;
var
   i,tg         :       longint;
   begin
        assign(f,fi); reset(f);
        readln(f,n);
        for i := 1 to n do
        begin
             readln(f,a[i].d,a[i].c);
             if a[i].d > a[i].c then
             begin
                  tg := a[i].d;
                  a[i].d := a[i].c;
                  a[i].c := tg;
             end;
        end;
        close(f);
   end;

procedure sapxep;
var
   i,j          :       longint;
   tg           :       dt;
   begin
        for i := 1 to n - 1 do
          for j := i + 1 to n do
          if a[i].d > a[j].d then
          begin
               tg := a[i];
               a[i] := a[j];
               a[j] := tg;
          end;
   end;

procedure qhd;
var
   i,j          :       longint;
   begin
        max := -1;
        for i := 1 to n do
        begin
             d[i] := 1;
             truoc[i] := 0;
             for j := i - 1 downto 1 do
             if (a[j].c <= a[i].d) and (d[j] + 1 > d[i])
then
             begin
                  d[i] := d[j] + 1;
                  truoc[i] := j;
             end;
             if d[i] > max then
             begin
                  max := d[i];
                  li := i;
             end;
        end;
   end;

procedure truy( i : integer );
   begin
        if truoc[i] <> 0 then truy(truoc[i]);
        writeln(g,a[i].d,' ',a[i].c);
   end;

procedure ghi;
   begin
        assign(g,fo); rewrite(g);
        writeln(g,max);
        truy(li);
        close(g);
   end;

BEGIN
     nhap;
     sapxep;
     qhd;
     ghi;
END.

Some notes : I write this program in Vietnamese. So here
are some translations :
nhap : read_data;
sapxep : sort;
qhd : DP;
ghi : write_output;
Hope you understand !!!
mailto : trungduck@yahoo.com



>     Can you tell me how to DP?
>     thank you.

I just took your solution and changed loop downto a little.
This will be accepted: (has already been:).
Mind that you don't have to use loop at all - just using
formula n*(n+1)/2 seperately for n>=1 and n<1 :)
I can post my solution here if you want, or send it by email

program p;
var i,n:longint;
    res:longint;
begin
  read(n);
  res := 0;
  if (n >=1) then
     for i:=1 to n do res := res + i
  else begin
     res:=1;
     for i:=1 to -n do res := res - i;
  end;
  write(res);
end.

> Since you know the solution,why don't you tell me or give
> me a reference program?