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On a table are N cards, with a positive integer printed on the front and back of each card (possibly different).

We flip any number of cards, and after we choose one card. 

If the number X on the back of the chosen card is not on the front of any card, then this number X is good.

What is the smallest number that is good?  If no number is good, output 0.

Here, fronts[i] and backs[i] represent the number on the front and back of card i

A flip swaps the front and back numbers, so the value on the front is now on the back and vice versa.


Input: fronts = [1,2,4,4,7], backs = [1,3,4,1,3]
Output: 2
Explanation: If we flip the second card, the fronts are [1,3,4,4,7] and the backs are [1,2,4,1,3].
We choose the second card, which has number 2 on the back, and it isn't on the front of any card, so 2 is good.



  1. 1 <= fronts.length == backs.length <= 1000.
  2. 1 <= fronts[i] <= 2000.
  3. 1 <= backs[i] <= 2000.

class Solution { public int flipgame(int[] fronts, int[] backs) { } }