What is the total number of office holders who preceded the people working under president bill clinton?
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/property/president> <http://dbpedia.org/resource/Bill_Clinton> . ?uri <http://dbpedia.org/property/successor> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/OfficeHolder>}
Bill_Clinton