#描述#
Given a sequence b1, b2, b3… bn of odd length, the occurrence of every bi (i=1, 2, 3…n) is an even number except one number, the P number, which occurs odd times. Your task is to find that P number.

#格式#
##输入格式##
The input file contains several test case, each test case starts with a line contains an odd number n (0&ltn&lt10 000), the length of the sequence, followed by a line with n numbers b1, b2, b3…bn. It is guaranteed that every bi (i=1, 2, 3..,n) can be represented by a signed integer. The input is terminated by a test case with n = 0. It should not be processed.

##输出格式##
For each test case, output a line the P number of the corresponding sequence.

#样例1#
##样例输入1##

5
2 3 2 3 4
7
2 2 2 2 2 2 2
0

##样例输出1##

4
2

#限制#
1000ms
32768KB

#提示#
O(n) algorithm exits.

#来源#
Limitfan