I can't figure out why this answer is wrong?

# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.
def num_teachers(teachers):
    count = 0
    for teach in teachers:
        count +=1
    return count

def num_courses(teachers):
    count1 = 0
    for value in teachers.values():
        count1 += int(len(value))
    return count1

def courses(teachers):
    list_of_all_courses = []
    for value in teachers.values():
        list_of_all_courses.extend(value)
    return list_of_all_courses


def most_courses(teachers):
    max_courses = max(teachers.values())
    for teacher in teachers:
        for value in teachers.values():
            if value == max_courses:
                return teacher