here is my programm
thanx
{1112}
var
  n,i,j,temp : integer;
  a          : array[1..100,1..2] of integer;
  b          : array[1..100,0..100,1..2] of integer;
begin
  readln(n);
  for i :=1 to n do
    begin
      readln(a[i,1],a[i,2]);
      if a[i,1]>a[i,2] then
      begin
      temp:=a[i,2];
      a[i,2]:=a[i,1];
      a[i,1]:=temp;
      end;
    end;
  a[n+1,1]:=1000;
  for i:=1 to n-1 do
    for j:=i+1 to n do
      if a[i,1]>a[j,1] then
        begin
          temp:=a[i,1];
          a[i,1]:=a[j,1];
          a[j,1]:=temp;
          temp:=a[i,2];
          a[i,2]:=a[j,2];
          a[j,2]:=temp;
        end;
  b[n,0,1]:=1;b[n,1,1]:=a[n,1];b[n,1,2]:=a[n,2];
  for i:=n-1 downto 1 do
    begin
      temp:=a[i,2];j:=i+1;
      while (temp>a[j,1]) and (i<n+1) do inc(j);
      if (j=n+1) then
        begin
          b[i,0,1]:=1;b[i,1,1]:=a[i,1];b[i,1,2]:=a[i,2];
        end
      else
        begin
          for temp:=1 to b[j,0,1] do
            begin
              b[i,temp,1]:=b[j,temp,1];
              b[i,temp,2]:=b[j,temp,2];
            end;
          b[i,0,1]:=b[j,0,1]+1;
          b[i,b[i,0,1],1]:=a[i,1];
          b[i,b[i,0,1],2]:=a[i,2];
        end;
    end;
  j:=1;temp:=-1;
  for i:=1 to n do
    if b[i,0,1]>temp then
      begin
        temp:=b[i,0,1];
        j:=i;
      end;
  writeln(b[j,0,1]);
  for i:=b[j,0,1] downto 1 do
    writeln(b[j,i,1],' ',b[j,i,2]);
end.