gistfile1.txt

def reproduce(m, f, target_m, target_f):
    stack = []
    generation = 0
    while True:
        generation += 1
        m1, f1 = m+f, f
        m, f = m, f+m

        success = m == target_m and f == target_f
        success = success or (m1 == target_m and f1 == target_f)

        if success:
            return generation

        impossible = m > target_m or f > target_f
        impossible = impossible or (m1 > target_m or f1 > target_f)

        if impossible:
            if len(stack):
                m, f, generation = stack.pop()
                continue
            return False

        stack.append((m1, f1, generation))

def answer(target_m, target_f):
    target_m, target_f = int(target_m), int(target_f)
    m = f = 1
    answer = reproduce(m, f, target_m, target_f)
    return (answer and '%d' % answer) or 'impossible'