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class Solution {
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  public int preimageSizeFZF(int k) {
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    long n = 4L * k;
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    int resp = 0;
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    while (true) {
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      int t = zeros(n);
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      if (t > k) return 0;
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      if (t == k) return 5;
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      n++;
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    }
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  }
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  private int zeros(long n) {
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    int resp = 0;
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    while (n > 0) {
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      resp += (int) (n / 5);
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      n /= 5;
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    }
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    return resp;
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  }
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}