#include <bits/stdc++.h>
#define REP(i,a,b) for(int i=(a);i<(b);i++)
#define RREP(i,a,b) for(int i=(a);i>=(b);i--)
typedef long long ll; typedef long double ld;
using namespace std;
const int INF=1e9, MOD=1e9+7, around[]={0,1,1,-1,-1,0,-1,1,0,0};
const ld PI=abs(acos(-1));
int a,c;

int main(){
	cin >> a >> c;
	
	int i=0;
	vector<int> vec;
	while((a>>i) or (c>>i)){
		if((a>>i)==1 and (c>>i)==1) vec.push_back(0);
		else if((a>>i)==1 and (c>>i)==0) vec.push_back(1);
		else if((a>>i)==0 and (c>>i)==1) vec.push_back(1);
		else vec.push_back(0);
		i++;
	}
	
	int tmp=1,pot=0;
	REP(i,0,vec.size()) pot+=vec[i]*tmp,tmp*=2;
	
	cout << pot << endl;
	return 0;
}