182861
Viterbo remained loyal to Frederick II , Holy Roman Emperor , and refused to admit Pope Gregory IX in 1232 .
 Viterbo, Frederick II , Holy Roman Emperor, Pope Gregory IX
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Viterbo, Frederick II , Holy Roman Emperor, Pope Gregory IX