# Given a string 'str', this counts all substrings with length 2 and print them
def countsubstrings(str):
    dict = {} # dictionary: key => substring , value => its frequency

    for i in range(len(str))
        substr = str[i:i+2] # substring with length 2
        if len(substr) < 2:
        continue

        # check if 'substr' is in count
        if dict.has_key(substr):
            dict[substr] += 1
        else:
           dict[substr] = 1

    return(dict)

if __name__ == '__main__':
    import sys
    str = sys.argv[1]
    # print str # for debug

    hash = countsubstrings(str)
    # print hash # for debug

    # sort dictionaries
    list = [ (hash[k], k) for k in hash.keys() ]
   list.sort()
    list.reverse()

    # print all substrings
    for (v, k) in list:
        print k, " occurs ", v, " times"