The square root of a number written in a text file

You need to create a program that will read a number from a file and calculate the root of that number and write the result to a new text file. The problem is that the wrong answer is output, tell me what the error is

 using (StreamReader sr = new StreamReader("file.txt"))
        {
            string numbers = sr.ReadLine();

            int countOfElements;
            int sqrtOfElement = 0;

            String[] number = numbers.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); 
            countOfElements = numbers.Length; 

            for (int count = 0; count < countOfElements; count++)
            {
                sqrtOfElement += Convert.ToInt32(Math.Sqrt(numbers[count])); 
            }

            File.WriteAllText("result.txt", sqrtOfElement.ToString());

            Console.WriteLine(sqrtOfElement);
       
            Console.ReadKey();
        }

If you write the number 9 in a text file, the result is 8 instead of 3