Code not working after submission

I have some trouble submitting my code. It works perfectly fine when I hit the run button but prompts me an error after submitting it. Please help me out on this one.
Contest Code : IARCSJUD | Problem Code : BOOKLIST

import java.util.*;
import java.lang.*;
import java.io.*;

class Codechef
    {

static Scanner sc = new Scanner(System.in);
static ArrayList<String> books;
static int r, t, temp;
static Map<Integer, String> map = new HashMap<>();

static void input(int n) {
	sc.nextLine();
	r = n;
	register();
}

static void register() {
	//System.out.println("Enter the books : ");
	books = new ArrayList<String> (Arrays.asList(sc.nextLine().split(" ")));
	//System.out.println("Enter the number of registers : ");
	t = sc.nextInt();
	for (int i = 0; i < t; i++) {
		//System.out.println("Enter the serial number of the book : ");
		temp = sc.nextInt();
		map.put(temp, books.get(temp - 1));
		books.remove(temp-1);
	}
	execute();
}

static void execute() {
	for (Integer a : map.keySet()) {
		System.out.println(map.get(a));
	}
}

public static void main(String[] args) {
	Codechef ob = new Codechef();
	//System.out.println("Enter the number of books : ");
	while(sc.hasNext()) 
	ob.input(sc.nextInt());
}

}