Find root of number - apply binary search - have a bug, and then fixed on line 29, instead of -1, return start/ 10000.0

FindRootOfNumber.cs

using System;

class Solution
{
    public static double Root(double x, int n)
    {
      if(x < 0 || n <= 0)
        return -1; 
      
      int start = 0; 
      int end   = (int)(Math.Max(1, x) * 10000); // 0.01 -> 0.1 
      
      while(start <= end)
      {
         int middle = start + (end - start)/ 2; 
        // middle - root(x, n) < 0.001
        
         double middleValue = Math.Pow(middle/ 10000.0, n); 
        
         if(Math.Abs(middleValue - x) < 0.001) /// not true, my anaylisy 
           return middle/ 10000.0; 
        
         if(middleValue < x)
           start = middle + 1; 
         else 
           end   = middle - 1; 
      }
      
      return start/ 10000.0; // x = 7, 0, 0.0001, 0.0002, ..., 1 using binary search 70,000 // bug found in web complier
    }

    static void Main(string[] args)
    {

    }
}
/*
keywords:
nonegative number x
n > 0 integer
error of 0.001 
  
ask: root of number, y ^ n = x
given example: x = 7, n = 3, find solution: 1.913 
  Abs(1.917 - root(x, n)) < 0.001
  Binary search -> 0.001
  0 - 7 lower bound/ upper bound
  increment value -> 0.0001 
  70000 to search, logn = 10 * log70 = 60 times 
  */