using System;

using System.Globalization;

public static class FloatExtension

{

    public static decimal RoundFirstSignificantDigit(this decimal input)

    {

                if (input == 0)

                    return input;

​

                // Split the input after the decimal to get the length

                var values = input.ToString(CultureInfo.InvariantCulture).Split('.');

                long firstValue = long.Parse(values[0]);

                long secondValue = long.Parse(values[1]);

                int precision = 0;

​

                if (secondValue.ToString().Length >= 3)

                {

                    int secondNumber = int.Parse(secondValue.ToString().Substring(1, 1));

                    int thirdNumber = int.Parse(secondValue.ToString().Substring(2, 1));

                    if (secondNumber < 5 && thirdNumber > 4)

                    {

                        precision = 1;

                    }

                }

​

                var val = input - Math.Round(input, 0);

                while (Math.Abs(val) < 1)

                {

                    val *= 10;

                    //Console.WriteLine(val);

                    precision++;

                    //Console.WriteLine(precision);

                }

                return Math.Round(input, precision);

    }

}       

public class Program

{

        public static void Main()

        {

            Console.WriteLine((49.103999999999999m).RoundFirstSignificantDigit());      

            Console.WriteLine((0.97399999999999998m).RoundFirstSignificantDigit());     

        }

}

​

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