query: SELECT DISTINCT ?item ?country ?years
  WHERE {      
    ?country wdt:P31 wd:Q3624078 ; wdt:P1906 ?office .
    ?item wdt:P31 wd:Q5 ; p:P39 ?posn .
    ?posn ps:P39 ?office ; pq:P580 ?start_date .
    FILTER NOT EXISTS { ?posn pq:P582 ?end_date }
    BIND(ROUND((NOW() - ?start_date)/365.2425) AS ?years)
  }
  ORDER BY ?start_date
  LIMIT 30