using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication2
{
    public class Test
    {
        public static void Main(string[] args)
        {
            var bills = new List<Bill>
            {
                new Bill {date = DateTime.Now.Date.AddDays(-5), bill = 111, value = 10000},
                new Bill {date = DateTime.Now.Date.AddDays(-4), bill = 111, value = 15000},
                new Bill {date = DateTime.Now.Date.AddDays(-4), bill = 222, value = 10000},
                new Bill {date = DateTime.Now.Date.AddDays(-5), bill = 333, value = 15000},
                new Bill {date = DateTime.Now.Date.AddDays(-5), bill = 444, value = 10000},
                new Bill {date = DateTime.Now.Date.AddDays(-5), bill = 555, value = 15000},
                new Bill {date = DateTime.Now.Date.AddDays(-1), bill = 222, value = 15000},
                new Bill {date = DateTime.Now.Date.AddDays(-1), bill = 111, value = 10000}
            };


            var clientBills = new List<ClientBill>
            {
                new ClientBill {LastName = "Иванов", billNumber = 111, city = "Москва"},
                new ClientBill {LastName = "Иванов", billNumber = 222, city = "Москва"},
                new ClientBill {LastName = "Петров", billNumber = 333, city = "не Москва"},
                new ClientBill {LastName = "Петров", billNumber = 444, city = "не Москва"},
                new ClientBill {LastName = "Сидоров", billNumber = 555, city = "Москва"}
            };

            var result =
                clientBills.Where(x => x.city == "Москва")
                    .Select(x => x.LastName)
                    .Distinct()
                    .ToDictionary(client => client,
                        client =>
                            clientBills.Where(x => x.LastName == client)
                                .Select(x => x.billNumber)
                                .Sum(
                                    bill =>
                                        bills.Select(x => x.bill)
                                            .Distinct()
                                            .Select(
                                                b =>
                                                    bills.Where(x => x.bill == b)
                                                        .OrderByDescending(x => x.date)
                                                        .FirstOrDefault())
                                            .Where(x => x.bill == bill)
                                            .Select(x => x.value)
                                            .FirstOrDefault())).Where(x => x.Value > 20000);
        }
    }

    public class Bill
    {
        public DateTime date { get; set; }
        public int bill { get; set; }
        public double value { get; set; }
    }

    public class ClientBill
    {
        public string LastName { get; set; }
        public int billNumber { get; set; }
        public string city { get; set; }
    }
}