using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string stringCamel = "EuAmoCsharp";

        string stringSnake = string.Concat(

                         stringCamel.Select((x, i) => i > 0 && char.IsUpper(x) ? "_" + x.ToString().ToLower() : x.ToString().ToLower())

                     ); 

        Console.WriteLine(stringSnake);

    }

}