(Should be really simple) LINQ question

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C#

LINQ

C#4.0

Hi, I thought I understood LINQ according to my book. I don't.

All I want to do is sum some numbers. My code is below. The bit that doesn't compile is obvious.
My question is what am I doing wrong? All I want to do is sum the numbers 1 + 2 + 5 - 1000 + 100 = -892 but I can't even do that.

Please please can someone help me out here.

Thank you

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

namespace ConsoleApplication7
{
    class C3
    {
        public C3(int foo) { Foo = foo; }
        public int Foo { get; set; }
    }

    class C2
    {
        public C2(List<C3> bar) { Bar = bar; }
        public List<C3> Bar { get; set; }
    }

    class C1
    {
        public C1(List<C2> baz) { Baz = baz; }
        public List<C2> Baz { get; set; }
    }


    class Program
    {
        public void Run()
        {
            C2 c2_1 = new C2(new List<C3> {new C3(1), new C3(2), new C3(5)});
            C2 c2_2 = new C2(new List<C3> { new C3(-1000), new C3(100) });

            C1 c1 = new C1(new List<C2>() { c2_1, c2_2 });

            //Answer = -892, but I can't even get the syntax right for it to compile
            var resultSum = c1.Baz.Select(x => x.Bar).Sum(y => y.Foo);

        }
        static void Main(String[] args)
        {
            new Program().Run();
        }
    }
}