```python
def num_teachers(dic):
    return len(dic)

def num_courses(dic):
     return len(sum(dic.values(), []))

def courses(dic):
    return set(sum(dic.values(), []))       #in the input they test on doesn't need set()

def most_courses(dic):
    output = (0, "")
    for i, j in dic.items():        #use iteritems() for Py 2.x
        if len(j) > output[0]:
            output = (len(j), i)
    return output[1]

def stats(dic):
    return [[i, len(j)] for i, j in dic.items()]        #use iteritems() for Py 2.x
```