#include<stdio.h>

int main()
{
    freopen("n00b.in","r",stdin);
    freopen("n00b.out","w",stdout);
    int a,b,c=0,t=0,i;
    scanf("%d%d",&a,&b);
    for(i=1;a || b ;i=i+i)
        {
	    if (a%2==1 && b%2==1)
		if (!t)
		    t=1;
		else
		    c+=i;
	    if (a%2!=b%2)
		if (t==0)
		    {
		    c+=i;
		    }
	    if (  !(a%2) &&  !(b%2) )
		if (t)
		    {
                    t=0;
		    c+=i;
		    }
            a/=2;
            b/=2;
        }
    if (t)
        c+=i;
    printf("%d",c);
    return 0;
}