Программа прерывает работу

import java.util.Scanner;
public class Calculator {
    public static int addition(int x, int y) {
        int result = x + y;
        return result;
    }
    public static int subtraction(int x, int y) {
        int result = x - y;
    return result;
    }
    public static int multiplication(int x, int y) {
    int result = x * y;
    return result;
    }
    public static int division(int x, int y) {
  int result = x / y;
  return result;
    }
    public static void main(String[] args) {
     Scanner scan = new Scanner(System.in);
     System.out.println("Enter the first number:");
      int firstNumber = scan.nextInt();
      System.out.println("Enter the second number:");
        int secondNumber = scan.nextInt();
        System.out.println("What action do you want to perform?");
        System.out.println("1. Addition");
        System.out.println("2. Subtraction");
        System.out.println("3. Multiplication");
        System.out.println("4. Division");
        int choice = scan.nextInt();
        int result = 0;
   switch (choice) {
            case 1:
            result = addition(firstNumber, secondNumber);
            break;
            case 2:
         result = subtraction(firstNumber, secondNumber);
        break;
         case 3:
                result = multiplication(firstNumber, secondNumber);
       break;
        case 4:
           if (secondNumber != 0) {
                    result = division(firstNumber, secondNumber);
                } else {
                 System.out.println("Division by zero is not allowed.");
               return; // Exit the program
                }
                break;
            default:
               System.out.println("Invalid choice.");
                return; // Exit the program
        }

        System.out.println("Result: " + result);
    }
}

int firstNumber = Integer.parseInt(scan.nextLine());
int secondNumber = Integer.parseInt(scan.nextLine());

int firstNumber = scan.nextInt();
scan.nextLine();
int secondNumber = scan.nextInt();
scan.nextLine();

String action = scan.next();
где firstNumber и secondNumber оставь как были..