Multiply Big Number - String and Text Processing

using System;
using System.Text;

namespace _07MultiplyBigNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            string num = Console.ReadLine().TrimStart('0');
            int multiplier = int.Parse(Console.ReadLine());

            if (multiplier==0)
            {
                Console.WriteLine(0);
                return;
            }

            StringBuilder result = new StringBuilder();

            int onMind = 0;

            for (int i = num.Length - 1; i >= 0; i--)
            {
                char curr = num[i];
                int currAsDigit = int.Parse(curr.ToString());
                int product = currAsDigit * multiplier + onMind;
                int lastDigit = product % 10;
                result.Append(lastDigit);
                onMind = product / 10;
            }

            if (onMind>0)
            {
                result.Append(onMind);
            }

            StringBuilder answer = new StringBuilder();

            for (int i = result.Length - 1; i >= 0; i--)
            {
                char curr = result[i];

                answer.Append(curr);
            }

            Console.WriteLine(answer.ToString());
        }
    }
}