#include <iostream>
#include <fstream>
#define mod 9901
using namespace std;
int c[524];
long a[524][524];
ifstream fin("culori.in");
ofstream fout("culori.out");
int main()
{int i,j,k,p,n;
    fin>>n;
    n=n*2-1;
    for(i=1;i<=n;i++)fin>>c[i];
    for(i=1;i<=n;i++)a[i][i]=1;

    for(p=2;p<n;p+=2)
    for(i=1;i<=n-p;i++)
    {j=i+p;
      if(c[i]==c[j])
        for(k=i+1;k<j;k++)
            if(c[i+1]==c[k])
            a[i][j]=(a[i][j]+a[i+1][k]*a[k+1][j])%mod;

    }
    fout<<a[1][n];


}