prob1.cs

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

class Prob1
{
  static void Main()
  {
    IEnumerable<int> nums =
      from num in Enumerable.Range(1, 1000-1)
      where num % 3 == 0 || num % 5 == 0
      select num;

    System.Console.WriteLine(nums.Sum());
  }
}