//*******************************************************
//*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; // i????+1
		*(*(p + j) + 1) += 1; // ??j??+1
		cin >> i >> j;
	}
	for (k = 0; k < n; k++) // ??

		// ???????0???n - 1??????????????
		if (*(*(p + k)) == 0 && *(*(p + k) + 1) == n - 1)
		{
			cout << k << endl; // ??
			flag = 0;
		}

	// ??????NOT FOUND
	if (flag)
		cout << "NOT FOUND" << endl;
	return 0;
}