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class Solution:
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    def smallestSubsequence(self, s: str, k: int, letter: str, repetition: int) -> str:
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        s = list(s)
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        stack = []
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        countAll = s.count(letter)
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        count = 0
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        for ind, i in enumerate(s):
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            while stack and stack[-1] > i:
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                if stack[-1] == letter and i != letter:
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                    if countAll + count - 1 < repetition:
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                        break
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                if len(stack) + len(s) - ind - 1 < k:
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                    break
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                if stack[-1] == letter:
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                    count -= 1
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                stack.pop()
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            stack.append(i)
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            if i == letter:
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                count += 1
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                countAll -= 1
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        temp = 0
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        while len(stack) + temp > k:
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            if stack[-1] == letter and count <= repetition:
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                temp += 1
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            if stack[-1] == letter:
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                count -= 1
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            stack.pop()
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        return "".join(stack) + temp * letter