#include <cstdio>
#include <algorithm>
using namespace std;
int l, r, a, b, ret;
int main () {
scanf("%d %d", &l, &r);
for(a = l; a <= r; a++)
for(b = a; b <= r; b++)
ret = max(ret, a ^ b);
printf("%d\n", ret);
return 0;
}
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