import random

def train(text, max_len=5):
    model = dict()
    for i in range(1, max_len+1):
        model[i] = dict()
        for k in range(len(text) - i - 1):
            if not text[k:k+i] in model[i]:
                 model[i][text[k:k+i]] = dict()
            if text[k+i] in model[i][text[k:k+i]]:
                model[i][text[k:k+i]][text[k+i]] += 1
            else:
                model[i][text[k:k+i]][text[k+i]] = 1
    return model

def query(model, previous):
    for l in range(len(previous), 0, -1):
        if previous[-l:] not in model[l]:
            continue
        freqs = model[l][previous[-l:]]
        return random.choices(list(freqs.keys()), list(freqs.values()))[0]