from itertools import count


mapping = {}
for letters, number in zip("bfpv cgjkqsxz dt l mn r".split(), count(1)):
    mapping.update({letter:number for letter in letters})


def soundex(word):
    word = word.lower()
    first, rest = word[0], word[1:]

    digits = []
    digit = mapping.get(first)
    for letter in rest:
        next_digit = mapping.get(letter)
        if next_digit is not None and next_digit != digit:
            digits.append(next_digit)
            if len(digits) == 3:
                break
        digit = next_digit
    else:
        digits.extend(0 for x in xrange(3 - len(digits)))

    return first + "".join(map(str, digits))


assert map(soundex, "euler gauss hilbert knuth lloyd lukasiewicz".split()) \
    == map(soundex, "ellery ghosh heilbronn kant ladd lissajous".split()) \
    == "e460 g200 h416 k530 l300 l222".split()