// C# program to implement
// Luhn algorithm
using System;

class GFG {
	
// Returns true if given 
// card number is valid
static bool checkLuhn(String cardNo)
{
	int nDigits = cardNo.Length;

	int nSum = 0;
	bool isSecond = false;
	for (int i = nDigits - 1; i >= 0; i--) 
	{

		int d = cardNo[i] - '0';

		if (isSecond == true)
			d = d * 2;

		// We add two digits to handle
		// cases that make two digits 
		// after doubling
		nSum += d / 10;
		nSum += d % 10;

		isSecond = !isSecond;
	}
	return (nSum % 10 == 0);
}

	// Driver code
	static public void Main()
	{
		String cardNo = "79927398713";
		if (checkLuhn(cardNo))
			Console.WriteLine("This is a valid card");
		else
			Console.WriteLine("This is not a valid card");
	
	}
}

public class King {
    fewf
}

using System;

class Yeet{
    public int value = 1;
    public override string ToString (){
        return value.ToString();
    }
}

class Bruh{
    public Yeet skeet;
    public override string ToString (){
        return skeet.ToString();
    }
}

class HelloWorld {
  static void Main() {
      Yeet yeet = new Yeet();
      Bruh bruh = new Bruh{ skeet = yeet };
      ++(yeet.value);
      Console.WriteLine(yeet);
      Console.WriteLine(bruh);
  }
}