def inc(pw):
    pw = list(pw)
    i = (- 1)
    while (pw[i] == 'z'):
        pw[i] = 'a'
        i -= 1
    pw[i] = next[pw[i]]
    return ''.join(pw)
def inc(pw):
    pw = list(pw)
    i = (- 1)
    while (pw[i] == 'z'):
        pw[i] = 'a'
        i -= 1
    pw[i] = next[pw[i]]
    return .join(pw)