class Solution {
    public ListNode mergeInBetween(ListNode list1, int a, int b, ListNode list2) {
        ListNode temp = list1;
        ListNode list2LastNode = list2; 
        while(list2LastNode.next != null){
            list2LastNode = list2LastNode.next;
        }
        
        int index = 0;
        ListNode removeStart = temp;
        ListNode removeEnd = temp;
        
        while(temp != null){
            if(index == a-1){
                removeStart = temp;
            }
            if(index == b){
                removeEnd = temp.next;
                break;
            }
            temp = temp.next;
            index++;
        }
        
        removeStart.next = list2;
        list2LastNode.next = removeEnd;
        return list1;
    }
}