public class Solution {
    public ListNode swapPairs(ListNode head) {
        // TODO: Write your code here
        if (head == null || head.Next == null)
            return head;

        var dummy = new ListNode(0);
        dummy.Next = head;
        var current = dummy;

        while (current.Next != null && current.Next.Next != null) {
            var first = current.Next;
            var second = current.Next.Next;
            current.Next = second;
            first.Next = second.Next;
            second.Next = first;
            current = first;
        }

        return dummy.Next;
    }
}