def showCatsNeighbourhood(src, dst):
    s, d = open(src, 'r'), open(dst, 'w')
    l2 = s.readline()
    l1 = '' 
    occurs = 0
    while len(l2) > 0 :
        l3 = s.readline()
        if l2.find("cat") >= 0 :
            d.write(l1)
            d.write(l2)
            d.write(l3)
            d.write("---\n")
            occurs = occurs + 1
        l1 = l2
        l2 = l3
    d.write("found "+str(occurs)+" cats\n")
    s.close(); d.close()