Plot XML API result

I am trying to print the results of this XML API call, but get a parse error on line 4:

syntax error, unexpected '->' (T_OBJECT_OPERATOR)

<?php
if( $xml = simplexml_load_file("http://ift.tt/1DXk0tG"))
{
  foreach($xml->avg-dni->monthly as $detail) 
  {   
    $jan = $detail->jan;
    $feb = $detail->feb;
    echo "$detail->";
  }
}
?>