Prime Quadruple

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace PrimeQuadrupleImplementation
{
    class Program
    {
        static int original;
        static void Main(string[] args)
        {
            Console.Title = "Prime Quadruple Implementation";
            int n = 0;
            A: Console.WriteLine("Please enter number from 13 to 10000000 only.");
            n = Convert.ToInt32(Console.ReadLine());
            original = n;
            if (n < 13 || n > 10000000)
            {
                goto A;
            } else
            {
                GenerateCount(n);
            }
            Console.ReadLine();
        }
        private static void GenerateCount(int n)
        {
            int a, b, c, d, counter = 0;
            a = n;
            b = n + 2;
            c = n + 6;
            d = n + 8;
            counter = Is_Prime(a) + Is_Prime(b) + Is_Prime(c) + Is_Prime(d);
            Primequadruple(counter, d, n);
        }
        private static void Primequadruple(int count, int Size, int n)
        {
            if (count != 4)
            {
                n = n - 1;
                GenerateCount(n);
            } else if (Size > original)
            {
                n--;
                GenerateCount(n);
            } else
            {
                Console.WriteLine("Output : {0}", Size.ToString());
            }
        }
        private static int Is_Prime(int Num)
        {
            int i;
            for (i = 2; i <= Num - 1; i++)
            {
                if (Num % i == 0)
                {
                    return 0;
                }
            }
            if (i == Num)
            {
                return 1;
            }
            return 0;
        }
    }
}