Text Processing - Multiply BigNumber

package com.company;


import java.util.*;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String firstNumber = scanner.nextLine();
        int secondNumber = Integer.parseInt(scanner.nextLine());

        int result = 0;
        int charAsDigit = 0;

        StringBuilder multiplied = new StringBuilder();

        for (int i = firstNumber.length() - 1; i >= 0; i--) {
            char currentDigit = firstNumber.charAt(i);
            charAsDigit = currentDigit - '0';

            result += charAsDigit * secondNumber;//9*9=81
            if (result > 9) {
                if (i == 0) {
                    int remainder = result % 10;
                    int leftDigit = (result - remainder) / 10;
                    multiplied.append(remainder);
                    multiplied.append(leftDigit);

                } else {
                    int remainder = result % 10;
                    multiplied.append(remainder);
                    int leftDigit = (result - remainder) / 10;

                    result = leftDigit;
                }
            } else {
                multiplied.append(result);
                result = 0;
            }


        }

        System.out.println(multiplied.reverse());


    }


}