int n=0;
int k1=0,k2=0,flag=0;
int sum1[100000];
int sum2[100000];
int main()
{
    //freopen("zozo.in","r",stdin);
    //freopen("zozo.out","w",stdout);
    scanf("%d",&n);
    //if (n==0) {printf("NOT FOUND\n"); return 0; }
    scanf("%d%d",&k1,&k2);
    while (!(k1==0 && k2==0))
    {
     sum1[k1+1]++; sum2[k2+1]++;
     scanf("%d%d",&k1,&k2);
    }
    flag=0;
    for (int i=1; i<=n; i++)
        if (sum1[i]==0)
        {
          if (sum2[i]==n-1)
          {
            flag=1;
            printf("%d\n",i-1);
            break;
          }
        }
    if (flag==0) printf("NOT FOUND\n");
    return 0;
}
