var     n,i,j,k,l,m,s   : longint;
        c               : array [1..256] of longint;
        a               : array [1..512, 1..512] of longint;
        f               : text;


begin
assign  (f, 'culori.in');
reset   (f);
readln  (f, n);
m        := n * 2 - 1;
for i := 1 to m do
    read(f, c[i]);
close   (f);

for i := 1 to m do a[i,i] := 1;

for l := 2 to m do
    if (l mod 2 <> 0) then // lucram pe impare pt ca pe pare oricum e 0;
        for i := 1 to m - l + 1 do
            begin
            j   := i + l - 1;
            if (c[i]=c[j]) then
                begin
                s   := 0;
                for k := i to j-1 do
                    if (c[i]=c[k]) then
                    s := (s + a[i+1, k] * a[k+1,j]) mod 9901;
                a[i,j]:= s;
                end;
            end;


assign  (f, 'culori.out');
rewrite (f);
writeln (f, a[1,m]);
close   (f);
end.