# Given a string 'str', this counts all substrings with length 2 and
# print them in decreasing order with their frequecies
def countsubstrings(str):
    '''
    count all substrings with length 2 and
    return count = [(n1, str1), (n2, str2), ...]
    the order is not considered
    '''
    count = []

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

        # check if 'substr' is in count

    return(count)

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

    count = countsubstrings(str)
    print count # for debug
    
    count.sort()
    count.reverse()

    # print all substrings in decreasing order with their frequencies
    for (n, s) in count:
        print s, " occurs ", n, " times"