using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var inputStr = "first/value_us";

        inputStr = Regex.Replace(inputStr, @"[^0-9a-zA-Z]+", "_")

            .ToUpperInvariant();

        if(!Enum.TryParse<vals>(inputStr, out var enumVal))

            throw new Exception("Invalid string value provided");

        Console.WriteLine((int)enumVal);

    }

    public enum vals

    {

        FIRST_VALUE =1,

        SECOND_VALUE =2,

        THIRD_VALUE =3

    }

}