from collections import defaultdict


def count_kmers(sequence, k):
    kmers_count = defaultdict(int)
    top_rng = len(sequence) - k + 1

    for i in range(0, top_rng):
        kmer = sequence[i:i + k]
        assert len(kmer) == 14, 'FAIL'
        kmers_count[kmer] += 1
    return kmers_count


def get_most_frequent_kmers(kmers):
    max_freq = max(kmers.itervalues())
    most_freq = (kmer for kmer, freq in kmers.iteritems() if freq == max_freq)
    return ' '.join(most_freq)


if __name__ == '__main__':
    with open('dataset_2_10.txt', 'r') as data:
        sequence = data.readline()
        k = int(data.readline())
    kmers = count_kmers(sequence, k)
    print get_most_frequent_kmers(kmers)