using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<BigInt> list = new List<BigInt>();

        list.Add(new BigInt() { i = 1});

        list.Add(new BigInt() { i = 2});

        list.Add(new BigInt() { i = 3});

​

        Console.WriteLine(list.Sum(b => b.i));

    }

}

​

public class BigInt

{

    public int i;

}