Quadronacci

long firstMember = long.Parse(Console.ReadLine());
        long secondMember = long.Parse(Console.ReadLine());
        long thirdMember = long.Parse(Console.ReadLine());
        long fourthMember = long.Parse(Console.ReadLine());
        int r = int.Parse(Console.ReadLine());
        int c = int.Parse(Console.ReadLine());
        int length = r * c;
        long[,] matrix = new long[r, c];
        List<long> massive = new List<long> { firstMember, secondMember, thirdMember, fourthMember };
        long fifthMember;
        for (int i = 4; i < length; i++)
        {
            fifthMember = firstMember + secondMember + thirdMember + fourthMember;
            firstMember = secondMember; secondMember = thirdMember; thirdMember = fourthMember; fourthMember = fifthMember;
            massive.Add(fifthMember);
        }
        long a = 0;
        for (int i = 0; i < r; i++)
        {
            for (int j = 0; j < c; j++)
            {
                matrix[i, j] = massive[a];
                a++;
            }
        }