n,l=input().split() n=int(n) l=int(l) a=[int(x) for x in input().split()] for i in range(1,n): if (a[i]>2*a[i-1]): a[i]=2*a[i-1] for i in range(n,31): a.append(2*a[i-1]) ans=0 while (l>0): bl=bin(l)[2:] lb=len(bl) if (min(a[lb:])<=a[lb-1]): ans+=min(a[lb:]) break ans+=a[lb-1] l-=pow(2,lb-1) print(ans)