OLOLO - Onotole needs your help
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.
Onotole has found not optimal AC algorithms, so all solutions will be rejudged. He is watching you.
Great Problem... Learnt something new...
Cool question, giving a hint would spoil it. But believe me, doing this one is worth it.
Java Guys: Fastest input handling will be required for this!
I don't know what the problemsetter considers to be a "not optimal algorithm", but anyway it isn't fair to reduce timelimit after several AC submissions (e.g. my Python solution). Decision about timelimit should be made BEFORE a problemset is published.