OLOLO - Onotole needs your help

输入 $n$ 和 $n$ 个数字，这 $n$ 个数字里只有一个数只出现了一次，求这个数。(保证只有一个数出现了一次)

 Onotole has a lot of pyani. Each pyani has a number, writing on it. Pyanis with equal numbers are indistinguishable. Onotole knows everything, so, he knows that each pyani appeared twice, and only one pyani is unique. He wants to get вздръжни эффект, and he needs the unique pyani. Given the list of pyanis denote which one of them appeared once (it is guaranteed that other pyanis appeared twice).

First line of input contains number of pyanis N <= 500 000. Next N lines contain a single positive integer 1 <= Pi <= 10^9.

Output one positive integer on pyani, which appeared once.

\n3\n1\n8\n1\n\n

8\n