using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {   

        var input = "JPR5AU75";

            Console.WriteLine(GetNumericValue(input,'R'));

            //Expected output=5

            Console.WriteLine(UpdateNumericValue(input, 'R', 7));

            //Expected output=JPR7AU75

​

            input = "PR2.9AU75";

            Console.WriteLine(GetNumericValue(input, 'R'));

            //Expected output=2.9

            Console.WriteLine(UpdateNumericValue(input, 'R', 3.5));

            //Expected output=PR3.5AU75

​

            input = "PKLR555AU75";

            Console.WriteLine(GetNumericValue(input, 'R'));

            //Expected output=555

            Console.WriteLine(UpdateNumericValue(input, 'R', 765));

            //Expected output=PKLR765AU75

            //Console.ReadLine();

            input = "ABCDEF";

            Console.WriteLine(GetNumericValue(input, 'C'));

            //Expected output=""

            Console.WriteLine(UpdateNumericValue(input, 'C', 42));

            //Expected output="ABCDEF"

            input = "ABCDEF";

            Console.WriteLine(GetNumericValue(input, 'F'));

            //Expected output=""

            Console.WriteLine(UpdateNumericValue(input, 'F', 42));

            //Expected output="ABCDEF"

            input = "666ABC666ABC555";

            Console.WriteLine(GetNumericValue(input, 'C'));

            //Expected output="666"

            Console.WriteLine(UpdateNumericValue(input, 'C', 42));

            //Expected output="666ABC42ABC555"

            input = "BR11.05AU17.51";

            Console.WriteLine(GetNumericValue(input, 'R'));

            //Expected output="666"

            Console.WriteLine(UpdateNumericValue(input, 'R', 7));

            //Expected output="666ABC42ABC555"

    }

    static string GetNumericValue(string input, char c)

    {

        Regex regex = new Regex(@$"{Regex.Escape(c.ToString())}([-+]?\d+\.?\d*)");

        var match = regex.Match(input);

        if (match.Success)

        {

            return match.Groups[1].Value;

        }

        return string.Empty;

    }

    static string UpdateNumericValue(string input, char c, double newVal)

    {

        var needle = $"{c}{GetNumericValue(input, c)}";

        if (!string.IsNullOrEmpty(needle))

        {

            var regex = new Regex(Regex.Escape(needle));

            return regex.Replace(input, $"{c}{newVal.ToString()}", 1);

        }

        return input;

    }

}