[StartCode]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp3
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Random random = new Random();
            int number = random.Next(0,101);
            int sum = 0;
            int multiple1 = 3;
            int multiple2 = 5;

            for (int i = number; i > 0; i--)
            {
                if (i % multiple1 == 0)
                {
                    sum += i;
                }
                else if (i % multiple2 == 0)
                {
                    sum += i;
                }
                else if (i == 0) { }
            }
            Console.WriteLine("Сумма всех чисел от 0 до " + number + " кратные " + multiple1 + " и " + multiple2 + " будет :" + (sum + number) );
        }
    }
}
[EndCode]