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class Solution {
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 public:
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  int mySqrt(int x) {
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    int s = 0, e = x, mid;
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    while (s < e) {
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      mid = s + (e - s) / 2;
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      if (e - s == 1) break;
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      long double sqr = (long double)mid * mid;
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      if (sqr <= x)
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        s = mid;
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      else
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        e = mid - 1;
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    }
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    if (e * e <= x)
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      return e;
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    else
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      return s;
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  }
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};
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```