const
  lim=550;
  base=9901;
var
  a:array[1..lim,1..lim] of longint;
  l,i,j,k,n:longint;
  q:array[1..lim] of longint;
begin
  assign(input,'culori.in');
  reset(input);
  readln(n); n:=(n shl 1) -1;
  for i:=1 to n do
  begin
    read(q[i]);
    a[i,i]:=1;
  end;
  close(input);
  l:=3;
  while (l<=n) do
  begin
    for j:=l to n do
    begin
      i:=j-l+1;
      if q[i]=q[j] then
      begin
        for k:=i+1 to j do
          if q[k]=q[i] then a[i,j]:=(a[i,j]+a[i+1,k-1]*a[k,j]) mod base;
      end;
    end;
    l:=l+2;
  end;
  assign(output,'culori.out');
  rewrite(output);
  writeln(a[1,n]);
  close(output);
end.