#include <iostream>
#include <fstream>
using namespace std;
const int mod=9901;
const int mod2=mod*mod;
const int nmax=517;
int v[nmax],dp[nmax][nmax];
int len,i,j,n,nr,prod;
int main()
{
    ifstream f("culori.in");
    ofstream g("culori.out");
    f>>n;nr=2*n-1;
    for(i=1;i<=nr;i++)
        f>>v[ i ];
    for(i=1;i<=nr;i++)
        dp[1][i]=1;
    for(len=2;len<=nr;len++)
        for(i=1;i<=nr-len+1;i++)
            if(v[i]==v[i+len-1])
    {
        for(j=i;j<=i+len-1;j++)
          if(v[j]==v[i])
            {
                dp[len][i]=(dp[len][i]+dp[j-i-1][i+1]*dp[len-j+i][j]);
                if(dp[len][i]>=mod2)
                    dp[len][i]-=mod2;
            }
        dp[len][i]%=mod;
    }
    g<<dp[nr][1];
    return 0;
}