// define variable which is used to check with its starting.
            int startsWith = 5;

            // Call the function which displays primes between 100<x<1000 and starts with 5
            DisplayThreeDigitPrimesStartsWith(startsWith);

            // Create the function
            void DisplayThreeDigitPrimesStartsWith(int startedNum)
            {
                // Iterate through 1000
                for (int i = 100; i < 1000; i++)
                {
                    // Check if the element prime and starts with the given value
                    if (CheckPrimeAndStart(i, startedNum))
                    {
                        // If true display it.
                        Console.WriteLine(i);
                    }
                }
            }

            // Create the function that check if the given num is prime and starts with the given value.
            bool CheckPrimeAndStart(int num, int startedNum)
            {
                var isStartWithFive = CheckStart(num, startedNum);

                if (!isStartWithFive)
                {
                    return false;
                }
                var isPrime = CheckPrime(num);

                if (!isPrime)
                {
                    return false;
                }
                return true;
            }

            bool CheckPrime(int num)
            {
                for (int i = 2; i < num; i++)
                {
                    if (num % i == 0)
                    {
                        return false;
                    }
                }
                return true;
            }

            bool CheckStart(int num, int checkedNumber)
            {
                var convertedPrime = num.ToString();

                var convertedCheckNumber = checkedNumber.ToString();

                if (!convertedPrime.StartsWith(convertedCheckNumber))
                {
                    return false;
                }
                return true;
            }