
int main()
{
	int n = 0;
	int num1[100000];
	int num2[100000];
	int flag[100000];
	int except[100000];
	int i = 0;
	int j = 0;
	int p = 0;
	int sum = 0;
	int f = 0;

	memset(num1,0,sizeof(num1));
	memset(num2,0,sizeof(num2));
	memset(flag,0,sizeof(flag));
	memset(except,0,sizeof(except));

	cin >> n;
	while (1)
	{
		cin >> num1[i] >> num2[i];
		except[num1[i]]++;
		if ((num1[i] == 0) && (num2[i] == 0))
			break;
		i++;
	}

	for (j = 0; j < n; j++)
	{
		if (except[j] != 0)
			continue;
		sum = 0;
		memset(flag,0,sizeof(flag));
		for (p = 0; p < i; p++)
		{
			if (num2[p] == j)
				if (flag[num1[p]] == 0)
					flag[num1[p]]++;
			if (num1[p] == j)
				flag[num1[p]] = -1;
		}
		for (p = 0; p < n; p++)
			sum += flag[p];
		if (sum == n - 1)
		{
			cout << j;
			f = 1;
		}
	}
	if (f == 0)
		cout << "NOT FOUND";

	return 0;
}