PROGRAMMING:Make a difference

This is a sign in question, very simple. A group of netizens are playing games on the Internet to see who is the most different. Everyone writes a number individually and then turns it in in turn. Whoever does not repeat the data with others wins. If many people are different, then the first thing they do is really different.
###Input format:
The input is a test case. First, the number of netizens n is given, and then n positive integers are given in turn. The given positive integers and N are not more than the 5th power of 10.
###Output format:
For each group of inputs, output the unique number. If not, output 'none'.
###Input sample 1:
Here is a set of inputs. For example:
```in
8 1 2 3 4 4 5 3 1
```
###Output sample 1:
The corresponding output is given here. For example:
```out
two
```
###Input sample 2:
Here is a set of inputs. For example:
```in
8 1 2 3 4 4 3 2 1
```
###Output sample 2:
The corresponding output is given here. For example:
```out
None
```






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