
int main ()
{ 
  int i,j,n,l;
  scanf("%d",&n);  
  int a[n],b[n];
  for (i=0;i<n;i++)
  {a[i]=0;b[i]=0;}
  scanf("%d %d",&i,&j);
  while ((i!=0)||(j!=0))
  { a[i]++;b[j]++;  
    scanf("%d %d",&i,&j);
  } 
  for (i=0;i<n;i++)
  if((a[i]==0)&&(b[i]==n-1))
  {printf("%d\n",i);l=0;}
  if (l==1)
  printf("NOT FOUND"); 

  

}

