from itertools import izip, starmap, tee
 
def pairwise(iterable): # itertools recipe
    a, b = tee(iterable)
    next(b, None)
    return izip(a, b)
 
def longest_duplicate(data):
    n = len(data)
    sa = sorted(xrange(n), key=lambda i: buffer(data, i)) # suffix array
    def lcp_item(i, j):  # find longest common prefix array item
        start = i
        while i < n and data[i] == data[i + j - start]:
            i += 1
        return i - start, start
    size, start = max(starmap(lcp_item, pairwise(sa)), key=lambda x: x[0])
    return data[start:start + size]
 
import sys
print longest_duplicate(sys.stdin.read())

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AAAAAAAAAAAAAAAAAAAAAAA hello world AAAAAAAAAAAAAAAAAAAAAAA
hello world hello world