C# BigNumbers on linked lists: calculating Factorial

BigNumber.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class Solution
{
    struct BigNumber
    {
        LinkedDigit data;

        public BigNumber(int value)
        {
            var input = GetAsRevertDigitArray(value);
            data = new LinkedDigit(input[0]);
            var current = data;
            foreach (var digit in input.Skip(1))
            {
                current.Next = new LinkedDigit(digit);
                current = current.Next;
            }
        }

        public void Multiply(int value)
        {
            var multiplyer = GetAsRevertDigitArray(value);
            var sum = new BigNumber(0);
            for (int i = 0; i < multiplyer.Length; i++)
            {
                var digit = multiplyer[i];
                var row = Copy();
                var currentDigit = row.data;

                while (currentDigit != null) {
                    currentDigit.Multiply(digit);
                    currentDigit = currentDigit.Next;
                }

                row.MoveBy10(i);
                sum.Append(row);
            }

            data = sum.data;
            Finalise();
        }

        public void Append(BigNumber other) {
            var currentA = this.data;
            var currentB = other.data;
            LinkedDigit previousA = null;

            while (currentA != null || currentB != null) {
                if (currentB == null) {
                    return;
                }

                if (currentA != null) {
                    currentA.Append(currentB.Value);
                } else {
                    currentA = new LinkedDigit(currentB.Value);
                    previousA.Next = currentA;
                }

                previousA = currentA;
				currentA = currentA?.Next;
                currentB = currentB?.Next;
            }
        }

        public void MoveBy10(int times)
        {
            for (int i = 0; i < times; i++)
            {
                var temp = data;
                data = new LinkedDigit(0);
                data.Next = temp;
            }
        }

        public string Print()
        {
            var result = "";

            var current = data;

            while (current != null)
            {
                result = current.Value + result;
                current = current.Next;
            }

            return result;
        }

		public BigNumber Copy()
		{
			var result = new BigNumber(data.Value);

			var current_new = result.data;
			var current = data.Next;

			while (current != null)
			{
				current_new.Next = new LinkedDigit(current.Value);
				current = current.Next;
				current_new = current_new.Next;
			}

			return result;
		}

        void Finalise() {
			var current = data;

			while (current != null)
			{
                current.Value += current.Addition;
				current = current.Next;
			}
        }

        class LinkedDigit
        {
            public byte Addition { get; set; }
            public byte Value { get; set; }
            public LinkedDigit Next { get; set; }

            public LinkedDigit(byte value)
            {
                Value = value;
            }

            public void Multiply(byte value)
            {
                var multiplication = Value * value;
                var ones = multiplication % 10;
                var tens = multiplication / 10;
                Value = 0;
                Append((byte)ones);

                if (tens > 0)
                {
                    if (Next == null)
                    {
                        Next = new LinkedDigit(0);
                    }
                    Next.Addition += (byte)tens;
                }
            }

            public void Append(byte value) {
                var sum = value + Value + Addition;
                Addition = 0;

                if (sum > 9) {
                    if (Next == null) {
                        Next = new LinkedDigit(0);
                    }
                    Next.Addition += 1;
                    Value = (byte)(sum % 10);
                } else {
                    Value = (byte)sum;
                }
            }
        }
    }

	static byte[] GetAsRevertDigitArray(int value)
	{
		byte n = 1;
		int tens = 10;

		while ((value / tens) > 0)
		{
			n++;
			tens *= 10;
		}

		var result = new byte[n];
		for (int i = n - 1; i >= 0; i--)
		{
			tens /= 10;
			result[i] = (byte)(value / tens);
			value -= result[i] * tens;
		}

		return result;
	}

	static void Main(String[] args)
	{
		int n = Convert.ToInt32(Console.ReadLine());
		var digit = new BigNumber(1);

		for (int i = 2; i <= n; i++)
		{
			digit.Multiply(i);
		}

		Console.Write(digit.Print());
	}
}