def occ(s1,s2):
    """occ (s1, s2) - returns the number of times that s2 occurs in s1"""
    count = 0
    start = 0
    while True:
        search = s1.find(s2,start)
        
        if search == -1:
            break
        else:
            count +=1
            start = search+1
    return count