const k=9901;
var f:text;
    j,i,n,h:integer;
    a:array[1..512,1..512] of integer;
    b:array[1..512] of integer;
    c:array[1..256,0..512] of integer;
    sol:array[1..512] of integer;
begin
assign(f,'culori.in');
reset(f);
readln(f,n);
for i:=1 to 2*n-1 do
    read(f,b[i]);
close(f);
sol[1]:=1;
for i:=1 to 2*n-1 do
  begin
    for j:=1 to c[b[i],0] do
      begin
        h:=c[b[i],j];
        a[i,i-h+1]:=a[i-1,i-h-1];
        sol[i]:=sol[i]+(a[i,i-h+1]*sol[h]) mod k;
      end;
  inc(c[b[i],0]);
  c[b[i],c[b[i],0]]:=i;
  a[i,1]:=1;
  end;

assign(f,'culori.out');
rewrite(f);
if b[1]<>b[2*n-1] then writeln(f,0)
else writeln(f,sol[2*n-1]);
close(f);
end.