//********************
//****??????****
//**?? 1100012915***
//*******12.13********
//********************
int main()
{
	int n, i, person1, person2 ;//n????i????????person1?2?????????
	int know[10000][2] = {0} ;	//???? ???????????????
	int *p ;
	int flag = 0 ;				//???????????
	p = &know[0][0] ;			//??p = know???...??????????
	cin >> n ;
	while ( 1 )
	{
		cin >> person1 >> person2 ;
		if ( ( person1 == 0 ) && ( person2 == 0 ) )
			break;				//??0 0?????
		*( p + person1 * 2 ) = *( p + person1 * 2 ) + 1 ;		//???????
		*( p + person2 * 2 +  1) = *( p + person2 * 2 + 1 ) + 1 ;//??ta?????
	}
	for ( i = 0 ; i <= n - 1 ; i++ )
		if ( ( *( p + i * 2 ) == 0 ) && ( *( p + i * 2 + 1 ) == n - 1 ) ) 
		{
			cout << i ;			//?????????????n-1????????????
			flag = 1 ;			//???????
		}
	if ( flag == 0 )
		cout << "NOT FOUND" ;	//?????"NOT FOUND"
	return 0;
}