Trying to calculate: there will be one server assigned to every 15 guests servers make 15$ an hour and $.50 every minute after an hour. Use the ceil function to round up

my work:

int guestNumber;

cout << "enter the number of guests: "

cin >> guest number;

// later on in the program

int serversNeeded = ceil(guestNumber % 15);

the program displays 11 but should display 2 (26 guests % 15 should be around 1.7 rounded up to 2, but again it's displaying 11) so what should I do to fix this?

thanks