Multiply big number

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _07.Multiply_Big_Number
{
    class Program
    {
        static void Main(string[] args)
        {
            var firstStr = Console.ReadLine();
            var secondStr = Console.ReadLine();

            var multiplyResult = 0;
            var reminder =0;
            string newNumber = string.Empty;
            for (int i = firstStr.Length-1; i>=0; i--)
            {

                int value = (firstStr[i] - 48) * (secondStr[0]-48) + reminder;
                //Console.WriteLine(value);
                if (value>9)
                {
                    reminder = value / 10; //Console.WriteLine(reminder);
                    value = value % 10;    //Console.WriteLine(value);
                }
                newNumber += value;

            }
            if (reminder != 0) newNumber += reminder;
            newNumber = new string(newNumber.Reverse().ToArray());
            Console.WriteLine(newNumber);
        }
    }
}