using System;
using System.Linq;
using System.Collections.Generic;
public class Program
{
public static void Main()
int? x =null;
int y = 5;
Console.WriteLine(x + y);
List<int?> ints = new List<int?>{null,null,2,3};
Console.WriteLine(ints.Sum());
ints = new List<int?>(){null,null,null,null};
}