#include<bits/stdc++.h>
using namespace std;
using ll =long long;

#include<atcoder/modint>
using namespace atcoder;
using mint=modint998244353;

void solve(){
	ll A,B;
	cin>>A>>B;
	ll an=0;
	for(ll x=0;x<=1000;x++)if((A^x)==B)an=x;
	cout<<an<<endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);


	int T=1;
	// cin>>T;
	while(T--)solve();
	
}