//*******************************************************
//*12.7??  ??????                               *
//*?????  ?? 1100012844                          *
//*???2011?12?10?                                 *
//*******************************************************
int main()
{
	int a[10000][2], n, i, j, k, flag = 1;
	int (*p)[2] = NULL;
	memset(a, 0, sizeof(a));
	p = a;
	cin >> n;
	cin >> i >> j;
	while (i != 0 || j != 0)
	{
		*(*(p + i)) += 1;
		*(*(p + j) + 1) += 1;
		cin >> i >> j;
	}
	for (k = 0; k < n; k++)
		if (a[k][0] == 0 && a[k][1] == n - 1)
		{
			cout << k << endl;
			flag = 0;
		}
	if (flag)
		cout << "NOT FOUND" << endl;
	return 0;
}