//****************************************************** 
/* ? ? ?   ???????
/* ? ?      ????                           
/* ? ? ? ??2010 ? 12  ?  13  ?     
/* ? ? ? ??????????????????????
???????????????
/* ? ?      ?1000012752        
*******************************************************/ 
int main()                                  
{
	int biaoji = 1;											//biaoji????????????
	int n;					
	int i,j;
	int a,b;
	int known[10000]={0},know[10000]={0};					//?????????know??????known
	cin >> n;
	for(i=0 ;  ; i++)
	{
		cin >> a >> b;										//????
		if(a==0 && b==0)									//??0?0??
			break;	
		if(a==b && a!=0)
			continue;
		know[a] = 1;										//????0?0????????????????????
		known[b]++;											//??????????
	}
	for(j=0 ; j<n ; j++)					
	{
		if(know[j] == 0 && known[j] == n-1)					//????????????????????n-1???????????
		{
			cout << j << endl;
			biaoji=0;
		}
	}

	if(biaoji)
		cout << "NOT FOUND" <<endl;
                  
    return 0;
}
                          
    
    
