N,M=map(int,input().split())
if N%2==0:
    print(N*M)
else:
    ans=M*(N-2)
    tmp=int("0b0"+"1"*len(bin(M)[3:]),2)
    ans+=tmp
    if M^tmp<=M:
        ans+=M^tmp
    else:
        ans=(N-1)*M
    print(ans)