/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param head the head of linked list.
     * @return an integer
     */
    public int countNodes(ListNode head) {
        // Write your code here
        int cnt = 0;
        while (head != null) {
            cnt ++;
            head = head.next;
        }
        return cnt;
    }
}