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class Solution {
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  public String thousandSeparator(int n) {
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    StringBuffer str = new StringBuffer(Integer.toString(n));
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    int index = str.length() - 3;
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    while (index >= 1) {
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      str.insert(index, '.');
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      index = index - 3;
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    }
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    return str.toString();
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  }
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}