Problem:
Score : 400 points

Problem Statement

In some other world, today is Christmas.

Mr. Takaha decides to make a multi-dimensional burger in his party. A level-L burger (L is an integer greater than or equal to 0) is the following thing:

A level-0 burger is a patty.

A level-L burger (L \geq 1) is a bun, a level-(L-1) burger, a patty, another level-(L-1) burger and another bun, stacked vertically in this order from the bottom.

For example, a level-1 burger and a level-2 burger look like BPPPB and BBPPPBPBPPPBB (rotated 90 degrees), where B and P stands for a bun and a patty.

The burger Mr. Takaha will make is a level-N burger. Lunlun the Dachshund will eat X layers from the bottom of this burger (a layer is a patty or a bun). How many patties will she eat?

Constraints

1 \leq N \leq 50

1 \leq X \leq ( the total number of layers in a level-N burger )

N and X are integers.

Input

Input is given from Standard Input in the following format:

N X

Output

Print the number of patties in the bottom-most X layers from the bottom of a level-N burger.

Sample Input 1

2 7

Sample Output 1

4

There are 4 patties in the bottom-most 7 layers of a level-2 burger (BBPPPBPBPPPBB).

Sample Input 2

1 1

Sample Output 2

0

The bottom-most layer of a level-1 burger is a bun.

Sample Input 3

50 4321098765432109

Sample Output 3

2160549382716056

A level-50 burger is rather thick, to the extent that the number of its layers does not fit into a 32-bit integer.

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

# encoding: utf-8
N, X = map(int, input().split())

L_child = 2 ** ((N - 1) + 2) - 3
P_child = 2 ** ((N - 1) + 1) - 1

def count(depth, pos):
    L_child = 2 ** ((depth - 1) + 2) - 3
    P_child = 2 ** ((depth - 1) + 1) - 1
    if depth == 0: return 1 # oh...
    # solved
    if pos == 0: return 0
    elif pos < L_child + 1: return count(depth - 1, pos - 1)
    elif pos == L_child + 1: return P_child + 1
    elif L_child + 1 < pos < 2 * (L_child + 1):
        return P_child + 1 + count(depth - 1, pos - (L_child + 2))
    else: return 2 * P_child + 1

print(count(N, X))