Name the president served by a lieutenant who succeeded Bob C Riley.
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/predecessor> <http://dbpedia.org/resource/Bob_C._Riley> . ?uri <http://dbpedia.org/ontology/lieutenant> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/President>}
Bob_C._Riley