Eighteen

 "She planned on having us guard a section, to which we will oversee the adventurers in our section. It's to reduce any possible casualties, or so she said." Tashirn answered.

 "Make sense," Catherine nodded in understanding, "Danger when exploring ruins or unknown Secret Realm cannot be completely avoided, but it is possible to reduce any would be casualties."

 The rest nodded, finding the reasoning of the Main Branch Leader to be thought out by her. Then again, if she could not even do such a thing, she would not gain the position of Main Branch Leader. 

 "Though, we are not allowed to bring anyone else, other than those who are allowed to explore the ruin." Tashirn said with a hint of disappointment.