n,m=map(int,input().split())
if n==1:
  print(0)
elif n%2==0:
  print(m*n)
else:
  ans=m*(n-1)
  f=x=0
  for i in range(30)[::-1]:
    if m>>i&1:
      f+=1
    else:
      if f>1:
        x|=1<<i
  print(ans+x*2)