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Collections: coding problems

Write a program that reads the input and prints the answer. Run checks it against every test, including hidden ones.

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A cashier scans product codes one after another. The store wants to know the first code that shows up for the second time, so it can check for a double scan.
Read the codes from left to right. Print the first code whose second copy you meet. If no code repeats, print none.
**Constraints:** 1 <= n <= 100000. Each code is an integer from -1,000,000,000 to 1,000,000,000.
Input. First line n. Second line n integers, separated by spaces.
Output. One line: the first repeated code, or `none`.
Example 1 input
```
5
3 1 4 1 5
```
Output
```
1
```
Example 2 input
```
4
1 2 3 4
```
Output
```
none
```
LanguageGo
package main import ( "bufio" "fmt" "os" ) func main() { reader := bufio.NewReader(os.Stdin) var n int fmt.Fscan(reader, &n) // your code here }