Hi All, I have a question. the code below passes almost all the tests except two, in which the number of given elements (n) is 20000. I suppose the code generates runtime error due to large number of elements, I just don't understand why.

import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    int n,d;
    List<List<Integer>> arr = new ArrayList<List<Integer>>();
    Scanner key = new Scanner(System.in);
    n = key.nextInt();
    for (int i=0;i<n;i++) {
        d = key.nextInt();
        for (int j=0;j<d;j++) {
            List<Integer> arr2 = new ArrayList<Integer>();
            arr.add(arr2);
            arr.get(i).add(key.nextInt());
        }
    }
    n = key.nextInt();
    for (int i=0;i<n;i++) {
        int x = key.nextInt()-1;
        int y = key.nextInt()-1;
        try {
        System.out.println(arr.get(x).get(y));
        }
        catch (Exception e)
        {
            System.out.println("ERROR!");
        }
    }
}

}