

int data[10000][10000] = {0};

int main()
{
	int n;
	cin >> n;
	int x, y;
	while(1)
	{
		cin >> x >> y;
		if (x == 0 && y == 0) break;
		data[x][y] = 1; // x??y?data[x][y] = 1
	}

	//??????????????
	x = 0;
	y = 1;
	while (y < n)
	{
		if (data[x][y] == 1) // x??y???x?????????y???????
		{
			x = y; // ??x
		}
		y ++; // y??
	}

	// ????????x????????????????
	int m;
	for (m = 0; m < n; m ++)
	{
		if (m == x) continue; // ??????????

		// ?????????x??x????????x?????????
		if (! (data[m][x] == 1 && data[x][m] == 0))
		{
			break;
		}
	}
	if (m == n) // ?n????????break?????x??????
		cout << x << endl;
	else // ??????????
		cout << "NOT FOUND" << endl;
	return 0;
}