Is there anyone who have already solved this problem?

[Problems][1]

Ikshu recently learnt to generate random numbers. He is generating stream binary numbers. Uptil now he has generated N bits of the binary number. Now, he wants to know if there is a streak of contiguous 1’s of length K.

Help him to find the probability of existence of such a streak in his binary number.

Assume that probability of generating a one and zero is equal i.e 0.5.

Input:

First and only line of input contains two space separated integers N and K as described above.

Output:

output contains one line containing probablity. output should be in n/m form where it is n/m is in its lowest fraction.

Constraints:

1<=N<=60

1<=K<=N

[1]: http://www.hackerearth.com/january-easy-challenge15/algorithm/ikshus-love-for-binary-numbers/