//*********************************************
//*?????????                        **
//*?????? 1100012914                   **
//*???2011.12.9                           **
//*********************************************


int main()
{
	int n, i, a, b, fam1[100000] = {0}, fam2[100000] = {0}, flag = 0, *p1, *p2;

	cin >> n;
	cin >> a >> b;
	while (!(a == 0 && b == 0))
	{
		fam1[a] = 1;
		fam2[b]++;
		cin >> a >> b;
	}
	p1 = fam1;
	p2 = fam2;
	for (i = 0; i < n; i++)
	{
		if (*(p1 + i) == 0 && *(p2 + i) == n - 1)
		{
			flag++;
			cout << i;
		}
	}
	if (flag == 0)
		cout << "NOT FOUND";
		return 0;
}