#include <iostream>
using namespace std;
typedef long long ll;
int main(void)
{
    ll a,b,res=0;
    ll ma=((ll)1)<<40;
    cin>>a>>b;
    bool cc=false;
    for(ll i=1;i<ma;i<<=1){
        ll m=i;
        bool aa=a&m;
        bool bb=b&m;
        if(aa&&bb&&cc){
            res|=m;
            cc=true;
        }
        else if(aa&&bb&&!cc||aa&&!bb&&cc||!aa&&bb&&cc){
            cc=true;
        }
        else if(aa&&!bb&&!cc||!aa&&!bb&&cc||!aa&&bb&&!cc){
            res|=m;
            cc=false;
        }else{
            cc=false;
        }
    }
    cout<<res<<endl;
    return 0;
}