6. Prime Pairs

using System;

namespace PrimePairs
{
    class Program
    {
        static void Main(string[] args)
        {
            // User input
            int firstStart = int.Parse(Console.ReadLine());
            int secondStart = int.Parse(Console.ReadLine());
            int diff1 = int.Parse(Console.ReadLine());
            int diff2 = int.Parse(Console.ReadLine());

            // Calculate threshold
            int firstEnd = firstStart + diff1;
            int secondEnd = secondStart + diff2;

            for ( int i = firstStart; i <= firstEnd; i++ )
            {
                for ( int j = secondStart; j <= secondEnd; j++ )
                {
                    // Assume number is prime by default
                    bool isPrime = true;
                    // Check if prime
                    for ( int k = 2; k < 10; k++ )
                    {
                        if ( i%k == 0 || j%k == 0 )
                        {
                            // If number can be divided by 2, 3, ..., 9 - not prime
                            isPrime = false;
                        }
                    }

                    // Print only prime numbers
                    if ( isPrime )
                    {
                        Console.WriteLine("{0}{1}", i, j);
                    }
                }
            }
        }
    }
}