13. Prime Pairs

using System;

namespace PrimePairs

{
    class Program
    {
        static void Main(string[] args)
        {
            int firstNum = int.Parse(Console.ReadLine());
            int secondNum = int.Parse(Console.ReadLine());
            int firstDiff = int.Parse(Console.ReadLine());
            int secondDiff = int.Parse(Console.ReadLine());

            for (int i = firstNum; i <= firstNum + firstDiff; i++)
            {
                for (int j = secondNum; j <= secondNum + secondDiff; j++)
                {
                    bool isFirstPrime = true;
                    bool isSecondPrime = true;

                    for (int k = 2; k <= Math.Sqrt(i); k++)
                    {
                        if (i % k == 0)
                        {
                            isFirstPrime = false;
                            break;
                        }
                    }
                    for (int k = 2; k <= Math.Sqrt(j); k++)
                    {
                        if (j % k == 0)
                        {
                            isSecondPrime = false;
                            break;
                        }
                    }
                    if (isFirstPrime && isSecondPrime)
                    {
                        Console.WriteLine($"{i}{j}");
                    }
                }
            }
        }
    }
}