ThreeDigitNaturalNumbers

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ThreeDigitNaturalNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            int numberN;
            int minNumberN = 1;
            int maxNumberN = 27;
            int firstFourDigitNumber = 1000;

            Random random = new Random();

            numberN = random.Next(minNumberN, maxNumberN + 1);

            int countThreeDigitNumber = 0;
            for (int i = numberN; i < firstFourDigitNumber; i += numberN)
            {
                if (i < firstFourDigitNumber)
                    countThreeDigitNumber++;
            }

            Console.Write($"Количество трехзначных натуральных чисел, которые кратны {numberN}: {countThreeDigitNumber}");
            Console.ReadKey();
        }
    }
}