/**
  *file  ????
  *author ???
  *date   12.10
  *function		?n??????????????????????????????? 
???????????????????????????????????????????? 
????????O(n)????
*/
int main()
{
	int n, a[10000], b[10000], i, j, flag = 0;						//a[i]?????i???????????b[i]??????????i?????
	cin >> n;
	memset(a,0,10000);memset(b,0,10000);
	while(1)
	{
		cin >> i >> j;
		if(i == 0 && j == 0)
		{
			break;
		}
		else
		{
			a[i]++;
			b[j]++;
		}
	}
	for(i = 0; i < n; i++)
	{
		if(a[i] == 0 && b[i] == n-1)
		{
			cout << i << endl;
			flag = 1;
		}
	}
	if(flag == 0)
	{
		cout << "NOT FOUND" << endl;
	}
	return 0;
}