using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var dict1 = new Dictionary<int, int> 

        {

            {1, 10},

            {2, 20},

            {3, 30}

        };

        var dict2 = new Dictionary<int, int> 

        {

            {1, 1},

            {2, 2},

            {4, 4}

        };

        var dicts = new List<Dictionary<int, int>>{ dict1, dict2 };

         var sommaEsigenze = dicts

                .SelectMany(d => d)

                .ToLookup(p => p.Key, p => p.Value)

                .ToDictionary(g => g.Key, g => g.Sum());

        foreach (var item in sommaEsigenze)

        {

            Console.WriteLine($"Id: {item.Key} - Value: {item.Value}");         

        }

    }

}