#include<stdio.h>

int a[550][550];
int i;
int s[550];
int k;
int n;
int j;



int main()
{
        freopen("culori.in","r",stdin);
        freopen("culori.out","w",stdout);
        scanf("%d",&n);
        n*=2;
        n-=1;
        for(i=1;i<=n;i++)
        {
                scanf("%d",&s[i]);
                a[i][i]=1;
        }
        for(i=1;i<=n;i++)
        {
                for(j=1;j<=n-i;j++)
                {
                        if (s[j]==s[i+j])
                        {
                                for(k=j+1;k<i+j;k++)
                                {
                                        a[j][i+j]=(a[j][i+j]+a[j+1][k]*a[k+1][i+j])%9901;
                                }
                        }
                }
        }

        printf("%d",a[1][n]);
        return 0;
        
}