package main

import . "fmt"

func main() {
	var n,m int
	Scan(&n,&m)
	ans := m*(n-n%2)
	if n%2 != 0 {
		tmp := m*(n-2)
		x := 0
		for i := 32; i>=0; i-- {
			b := 1<<i
			if b <= m {
				x = b
				break
			}
		}
		y := m^x
		for i := 32; i >= 0; i-- {
			b := 1 << i
			if b <= y && (y&b) == 0 {
				x |= b
				y |= b
			}
		}
		if x <= m && y <= m {
			tmp += x+y
			ans = max(ans, tmp)
		}
	}
	Println(ans)
}