Both Cases Stretch

Easy

Call a string **paired** if every letter that occurs in it occurs in both lowercase and uppercase. For example, cCdDd is paired, while cCd is not, because it has no uppercase D. Given a string text of English letters, find its longest contiguous piece that is a paired string and return it. If several pieces share the maximum length, return the one that starts first. If there is no paired piece at all, return an empty string.

Example 1

text="xKkqQkz" → 'KkqQk'

In KkqQk the letter k appears as both K and k, and q as both q and Q. Neither x nor z can be added, since their other case is missing.

Example 2

text="aAxbB" → 'aA'

Both aA and bB qualify with length 2, so the one that starts earlier is returned.

Example 3

text="Mn" → ''

No letter has its pair, so the answer is the empty string.

Constraints

1 ≤ len(text) ≤ 100
text consists of lowercase and uppercase English letters

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Input

text="xKkqQkz"

Expected

'KkqQk'

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