import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

N,K,*A = map(int,read().split())

wt = np.zeros(1<<N,np.int32)

for i,x in enumerate(A):
    wt[1<<i:1<<i+1] = wt[:1<<i] + x

answer = wt[wt <= K].max()
print(answer)