code: public static function thumbnailToId(string $thumbnailUrl): string
      {
          if (1 !== \preg_match('/\/([\d]+)\/([\d]+)(\-avatar\.jpg)$/', $thumbnailUrl, $match)) {
              throw new \RuntimeException(\vsprintf('Invalid thumbnail URL "%s"', [
                  $thumbnailUrl,
              ]));
          }
  
          return ltrim($match[1].$match[2], '0');
      }
docs: Returns a character's unique ID from a thumbnail URL.
  
  @param string $thumbnailUrl
  
  @return string