#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <memory.h>
#include <ctime>

using namespace std;

#define ABS(a) ((a>0)?a:-(a))
#define MIN(a,b) ((a<b)?(a):(b))
#define MAX(a,b) ((a<b)?(b):(a))
#define FOR(i,a,n) for (int i=(a);i<(n);++i)
#define FI(i,n) for (int i=0; i<(n); ++i)
#define pnt pair <int, int>
#define mp make_pair
#define PI 3.14159265358979
#define MEMS(a,b) memset(a,b,sizeof(a))
#define LL long long
#define U unsigned

LL solveStupid(LL l, LL r)
{
    LL res=0;
    for (LL i=l; i<=r; ++i)
        for (LL j=i; j<=r; ++j)
            res=max(res,i^j);
    return res;
}
string s1,s2;
LL dp[70][2][2][2][2];

LL rec(int p, int fl1, int fl2, int fr1, int fr2)
{
    if (p==s1.size())
        return 0;
    if (dp[p][fl1][fl2][fr1][fr2]!=-1)
        return dp[p][fl1][fl2][fr1][fr2];
    int min1=0,max1=1;
    if ((fl1==0) && (s1[p]=='1'))
        min1=1;
    if ((fl2==0) && (s2[p]=='0'))
        max1=0;
    int min2=0,max2=1;
    if ((fr1==0) && (s1[p]=='1'))
        min2=1;
    if ((fr2==0) && (s2[p]=='0'))
        max2=0;
    LL res=0;
    FOR(i,min1,max1+1)
        FOR(j,min2,max2+1)
        {
            int v=(i^j);
            LL toadd=0;
            if (v==1)
            {
                int step=s1.size()-p-1;
                toadd=(1ll<<step);
            }
            int nfl1=fl1,nfl2=fl2,nfr1=fr1,nfr2=fr2;
            if (i>s1[p]-'0')
                nfl1=1;
            if (i<s2[p]-'0')
                nfl2=1;
            if (j>s1[p]-'0')
                nfr1=1;
            if (j<s2[p]-'0')
                nfr2=1;
            res=max(res,toadd+rec(p+1,nfl1,nfl2,nfr1,nfr2));
        }
    return dp[p][fl1][fl2][fr1][fr2]=res;
}
string getbin(LL num)
{
    string res="";
    while (num)
    {
        res+=((num&1)+'0');
        num/=2;
    }
    reverse(res.begin(),res.end());
    return res;
}
LL solveSmart(LL l, LL r)
{
    s1=getbin(l);
    s2=getbin(r);
    while (s1.size()<s2.size())
        s1="0"+s1;
    MEMS(dp,-1);
    LL res=rec(0,0,0,0,0);
    return res;
}
int main()
{
#ifdef Fcdkbear
    freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    double beg=clock();
#endif
   LL l,r;
   cin>>l>>r;
   cout<<solveSmart(l,r)<<endl;

#ifdef Fcdkbear
    double end=clock();
    fprintf(stderr,"*** Total time = %.3lf ***\n",(end-beg)/CLOCKS_PER_SEC);
#endif
    return 0;
}