Step 10 of 12 · Frequency maps

First unique character

IntermediateJavaScript1,000 ms

Problem

Read one lowercase word and return its first character that appears exactly once. Return "None" when every character repeats.

Input

One lowercase word with no spaces.

Output

The first non-repeating character, or the exact word "None".

Examples

Input
swiss
Output
w

s repeats, while w is the first character seen exactly once.

Input
aabb
Output
None

Every character appears more than once.

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Define solve(input) and return the exact output. Network access is blocked and the runner stops after 1,000 ms. Run the example to inspect local console.log output.

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