function EntryNodeOfLoop(pHead)
{
    // write code here
    if(pHead == null){
        return 1;
    }
    if(pHead.next == null){
        return null;
    }
    var fast = pHead;
    var slow = pHead;
    while(slow != null && fast.next != null){
        slow = slow.next;
        fast = fast.next.next;
        if(fast == slow) break;
    }
     
    var p1 = slow;
    var p2 = pHead;
    while(p1 != p2){
        p1 = p1.next;
        p2 = p2.next;
    }
    return p1;
}