<?php

class ListNode{

    var $val;

    var $next = NULL;

    function __construct($x){

        $this->val = $x;

    }

}

function Merge($pHead1, $pHead2) {

    if ($pHead1===null) {

        return $pHead2;

    }

    if ($pHead2===null) {

        return $pHead1;

    }

    if ($pHead1->val < $pHead2->val) {

        $pHead1->next = Merge($pHead1->next, $pHead2);

        return $pHead1;

    }

    $pHead2->next = Merge($pHead1, $pHead2->next);

    return $pHead2;

}