task 6

using System;

public class Program
{
    public static void Main(string[] args)
    {
        int numberMax = 100;
        int numberMultipleFirst = 3;
        int numberMultipleSecond = 5;
        int numbersSum = 0;

        int numberRandom = Random.Shared.Next(numberMax);

        for (int numberStart = 0; numberStart < numberRandom; ++numberStart)
            if (numberStart % numberMultipleFirst == 0 ||
                numberStart % numberMultipleSecond == 0)
                numbersSum += numberStart;

        Console.WriteLine("Max number is : " + numberMax);
        Console.WriteLine("Random number is : " + numberRandom);
        Console.WriteLine("Sum of numbers is : " + numbersSum);
    }
}