package main

import . "fmt"

func main() {
	var n,m int
	Scan(&n,&m)
	if n == 1 {
		Println(0)
		return
	} else if n % 2 == 0 {
		Println(n*m)
		return
	}
	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 (m&b) == 0 && (x|b)<=m && (y|b) <= m {
			x |= b
			y |= b
		}
	}
	ans := m*(n-1)
	if (x^y^m)==0 && x <= m && y <= m {
		ans = max(ans, m*(n-2) + x+y)
	}
	x = 0
	for i := 32; i >= 0; i-- {
		b := 1 << i
		if b <= m-1 {
			x = b
			break
		}
	}
	y = (m-1)^x
	for i := 32; i >= 0; i-- {
		b := 1 << i
		if ((m-1)&b)==0 && (x|b) <= m && (y|b) <= m {
			x |= b
			y |= b
		}
	}
	if (x^y^(m-1))==0 && x <= m && y <= m {
		ans = max(ans, m*(n-3)+x+y+(m-1))
	}
	Println(ans)
}