fun main(args: Array<String>) {
    val (a,c) = readLine()!!.split(" ").map { it.toLong() }
    var ans = 0L
    for(i in 0..63) {
        val n = (1L shl i)
        if(a and n == 0L) {
            if(c and n != 0L) {
                ans += n
            }
        } else if(c and n == 0L) {
            ans += n
        }
    }
    println(ans)
}