Calculate marks

import java.util.*;
  class New{
      public static void main(String args[]){
      Scanner input = new Scanner(System.in);
          System.out.print("Enter Student Name : ");
          String name = input.next();
          
          System.out.print("Enter Student Address : ");
          String address = input.next();
          
          System.out.print("Enter Number of Subjects : ");
          int number_of_subjects = input.nextInt();
          
          int marks = 0;
          int max = 0;
          int total = 0;
          System.out.println();
              for(int i = 0 ; i < number_of_subjects ; i++){
          System.out.print("Enter Subject " + (i + 1) + " Marks : ");
          marks = input.nextInt();
          if(max < marks){
            max = marks;
          }
          total = total + marks;
          }
          boolean flag = true;
          while(flag){
                System.out.println();
                System.out.println("A. Show Student Details.");
                System.out.println("B. Show Maximum Marks.");
                System.out.println("C. Show Result.");
                System.out.println("X. Exit");
                System.out.println();
                System.out.print("Please select one option : ");
                String letter = input.next();
                System.out.println();
                
                    switch(letter){
                    case "A":
                    System.out.println("Student Name : " + name);
                    System.out.println("Student Address : " + address);
                    break;
                    case "B":
                    System.out.println("Maximum Marks : " + max);
                    break;
                    case "C":
                    double average = (double)total /
                    number_of_subjects;
                    String result = "Fail";
                    if(average >= 50){
                      result = "Pass";
          }
                    System.out.println("Result : " + result);
                    break;
                case "X":
                System.out.println("Good Bye......");
                flag = false;
                        break;
                        default :
                          System.out.println("Please select valid option");
}
}
}
}