Single Number (XOR)

Given a non-empty array where every element appears twice except for one, find that single element. Use XOR: a ^ a = 0, a ^ 0 = a. XOR all numbers together. Example: [4,1,2,1,2] → 4 (1^1=0, 2^2=0, 4^0=4)

Input

Line 1: n. Line 2: n space-separated integers.

Output

The single number.

Sample

5
4 1 2 1 2

Expected

4