How to extract following xml using PHP

 <id>rfBRFK4d1s</id>
  <first-name>Thamaraiselvam</first-name>
  <last-name>T</last-name>
  <headline>Software Development Intern at Snowman Branding Services Pvt. Ltd</headline>
  <picture-url>http://ift.tt/1yPKBAc;
  <industry>Computer Software</industry>
  <connections total="771" count="767" start="0">
    <person>
      <id>Fvq7UCM43W</id>
      <first-name>Mike</first-name>
      <last-name>Ryan</last-name>
      <headline>CEO / Advisor / VC Backed Startups  @mikegordonryan</headline>
      <picture-url>http://ift.tt/19qESw1;
      <api-standard-profile-request>
        <url>http://ift.tt/1yPKBAe;
        <headers total="1">
          <http-header>
            <name>x-li-auth-token</name>
            <value>name:LOn8</value>
          </http-header>
        </headers>
      </api-standard-profile-request>
      <site-standard-profile-request>
        <url>http://ift.tt/19qEUnu;
      </site-standard-profile-request>
      <location>
        <name>San Francisco Bay Area</name>
        <country>
          <code>us</code>
        </country>
      </location>
      <industry>Information Technology and Services</industry>
    </person>
    <person>
      <id>fvab8bjKXC</id>
      <first-name>Krishna</first-name>
      <last-name>Murari</last-name>
      <headline>PHP Web Developer at Unified Media Marketing Group</headline>
      <picture-url>http://ift.tt/1yPKB3j;
      <api-standard-profile-request>
        <url>http://ift.tt/19qEUnw;
        <headers total="1">
          <http-header>
            <name>x-li-auth-token</name>
            <value>name:oBCf</value>
          </http-header>
        </headers>
      </api-standard-profile-request>
      <site-standard-profile-request>
        <url>http://ift.tt/1yPKBAg;
      </site-standard-profile-request>
      <location>
        <name>New Delhi Area, India</name>
        <country>
          <code>in</code>
        </country>
      </location>
      <industry>Internet</industry>
    </person>

I'm trying to extract above xml using PHP and i tried with following code

$xml_response="my xml contents";
$xml = simplexml_load_string($xml_response);
echo $xml->person[0]['headers'] . "<br>";
echo $xml->id;

I can get id but i cannot get other things and

echo $xml->first-name; 

it shows error because of that - between first and name then i have so many category like person details how do i create loop for that to retrieve?